Specialized prefrontal "auditory fields": organization of primate prefrontal-temporal pathways

Click train elicited local gamma synchrony: Differing performance and pharmacological responsivity of primary auditory and prefrontal cortices

Auditory neural networks in the brain naturally entrain to rhythmic stimuli. Such synchronization is an accessible index of local network performance as captured by EEG. Across species, click trains delivered ∼ 40 Hz show strong entrainment with primary auditory cortex (Actx) being a principal source. Imaging studies have revealed additional cortical sources, but it is unclear if they are functionally distinct. Since auditory processing evolves hierarchically, we hypothesized that local synchrony would differ between between primary and association cortices. In female SD rats (N = 12), we recorded 40 Hz click train-elicited gamma oscillations using epidural electrodes situated at two distinct sites; one above the prefrontal cortex (PFC) and another above the Actx, after dosing with saline (1 ml/kg, sc) or the NMDA antagonist, MK801 (0.025, 0.05 or 0.1 mpk), in a blocked crossover design. Post-saline, both regions showed a strong 40 Hz auditory steady state response (ASSR). The latencies for the N1 response were ∼ 16 ms (Actx) and ∼ 34 ms (PFC). Narrow band (38-42 Hz) gamma oscillations appeared rapidly (<40 ms from stim onset at Actx but in a more delayed fashion (∼200 ms) at PFC. MK801 augmented gamma synchrony at Actx while dose-dependently disrupting at the PFC. Event-related gamma (but not beta) coherence, an index of long-distance connectivity, was disrupted by MK801. In conclusion, local network gamma synchrony in a higher order association cortex performs differently from that of the primary auditory cortex. We discuss these findings in the context of evolving sound processing across the cortical hierarchy.

Individualized Closed-Loop Acoustic Stimulation Suggests an Alpha Phase Dependence of Sound Evoked and Induced Brain Activity Measured with EEG Recordings

Following repetitive visual stimulation, post hoc phase analysis finds that visually evoked response magnitudes vary with the cortical alpha oscillation phase that temporally coincides with sensory stimulus. This approach has not successfully revealed an alpha phase dependence for auditory evoked or induced responses. Here, we test the feasibility of tracking alpha with scalp electroencephalogram (EEG) recordings and play sounds phase-locked to individualized alpha phases in real-time using a novel end-point corrected Hilbert transform (ecHT) algorithm implemented on a research device. Based on prior work, we hypothesize that sound-evoked and induced responses vary with the alpha phase at sound onset and the alpha phase that coincides with the early sound-evoked response potential (ERP) measured with EEG. Thus, we use each subject's individualized alpha frequency (IAF) and individual auditory ERP latency to define target trough and peak alpha phases that allow an early component of the auditory ERP to align to the estimated poststimulus peak and trough phases, respectively. With this closed-loop and individualized approach, we find opposing alpha phase-dependent effects on the auditory ERP and alpha oscillations that follow stimulus onset. Trough and peak phase-locked sounds result in distinct evoked and induced post-stimulus alpha level and frequency modulations. Though additional studies are needed to localize the sources underlying these phase-dependent effects, these results suggest a general principle for alpha phase-dependence of sensory processing that includes the auditory system. Moreover, this study demonstrates the feasibility of using individualized neurophysiological indices to deliver automated, closed-loop, phase-locked auditory stimulation.

The meso-connectomes of mouse, marmoset, and macaque: network organization and the emergence of higher cognition

The recent publications of the inter-areal connectomes for mouse, marmoset, and macaque cortex have allowed deeper comparisons across rodent vs. primate cortical organization. In general, these show that the mouse has very widespread, "all-to-all" inter-areal connectivity (i.e. a "highly dense" connectome in a graph theoretical framework), while primates have a more modular organization. In this review, we highlight the relevance of these differences to function, including the example of primary visual cortex (V1) which, in the mouse, is interconnected with all other areas, therefore including other primary sensory and frontal areas. We argue that this dense inter-areal connectivity benefits multimodal associations, at the cost of reduced functional segregation. Conversely, primates have expanded cortices with a modular connectivity structure, where V1 is almost exclusively interconnected with other visual cortices, themselves organized in relatively segregated streams, and hierarchically higher cortical areas such as prefrontal cortex provide top-down regulation for specifying precise information for working memory storage and manipulation. Increased complexity in cytoarchitecture, connectivity, dendritic spine density, and receptor expression additionally reveal a sharper hierarchical organization in primate cortex. Together, we argue that these primate specializations permit separable deconstruction and selective reconstruction of representations, which is essential to higher cognition.

Hyperphosphorylated tau in Alzheimer's disease disseminates along pathways predicted by the Structural Model for Cortico-cortical Connections

In Alzheimer´s disease (AD), hyperphosphorylated tau spreads along the cerebral cortex in a stereotypical pattern that parallels cognitive deterioration. Tau seems to spread transsynaptically along cortico-cotical pathways that, according to synaptic tract-tracing studies in nonhuman primates, have specific laminar patterns related to the cortical type of the connected areas. This relation is described in the Structural Model. In the present article, we study the laminar distribution of hyperphosphorylated tau, labeled with the antibody AT8, along temporal cortical types in postmortem human brains with different AD stages to test the predictions of the Structural Model. Brains from donors without dementia had scant AT8-immunorreactive (AT8-ir) neurons in allo-, meso-, and isocortical types. In early AD stages, the mesocortical dysgranular type, including part of the transentorhinal cortex, had the highest AT8 immunostaining and AT8-ir neurons density. In advanced AD stages, AT8 immunostaining increased along the isocortical types until reaching the auditory koniocortex. Regarding laminar patterns, in early AD stages there were more AT8-ir neurons in supragranular layers in each de novo involved neocortical type; in advanced AD stages, AT8-ir neurons were equally distributed in supra- and infragranular layers. These AT8-ir laminar patterns are compatible with the predictions of the Structural Model. In summary, we show that hyperphosphorylated tau initially accumulates in allo-, meso-, and isocortical types, offer a proof of concept for the validity of the Structural Model to predict synaptic pathway organization in the human cerebral cortex, and highlight the relevance of nonhuman primate tract-tracing studies to understand human neuropathology.

Unambiguous identification of asymmetric and symmetric synapses using volume electron microscopy

The brain contains thousands of millions of synapses, exhibiting diverse structural, molecular, and functional characteristics. However, synapses can be classified into two primary morphological types: Gray's type I and type II, corresponding to Colonnier's asymmetric (AS) and symmetric (SS) synapses, respectively. AS and SS have a thick and thin postsynaptic density, respectively. In the cerebral cortex, since most AS are excitatory (glutamatergic), and SS are inhibitory (GABAergic), determining the distribution, size, density, and proportion of the two major cortical types of synapses is critical, not only to better understand synaptic organization in terms of connectivity, but also from a functional perspective. However, several technical challenges complicate the study of synapses. Potassium ferrocyanide has been utilized in recent volume electron microscope studies to enhance electron density in cellular membranes. However, identifying synaptic junctions, especially SS, becomes more challenging as the postsynaptic densities become thinner with increasing concentrations of potassium ferrocyanide. Here we describe a protocol employing Focused Ion Beam Milling and Scanning Electron Microscopy for studying brain tissue. The focus is on the unequivocal identification of AS and SS types. To validate SS observed using this protocol as GABAergic, experiments with immunocytochemistry for the vesicular GABA transporter were conducted on fixed mouse brain tissue sections. This material was processed with different concentrations of potassium ferrocyanide, aiming to determine its optimal concentration. We demonstrate that using a low concentration of potassium ferrocyanide (0.1%) improves membrane visualization while allowing unequivocal identification of synapses as AS or SS.

The connectivity of the human frontal pole cortex, and a theory of its involvement in exploit versus explore

The frontal pole is implicated in humans in whether to exploit resources versus explore alternatives. Effective connectivity, functional connectivity, and tractography were measured between six human frontal pole regions and for comparison 13 dorsolateral and dorsal prefrontal cortex regions, and the 360 cortical regions in the Human Connectome Project Multi-modal-parcellation atlas in 171 HCP participants. The frontal pole regions have effective connectivity with Dorsolateral Prefrontal Cortex regions, the Dorsal Prefrontal Cortex, both implicated in working memory; and with the orbitofrontal and anterior cingulate cortex reward/non-reward system. There is also connectivity with temporal lobe, inferior parietal, and posterior cingulate regions. Given this new connectivity evidence, and evidence from activations and damage, it is proposed that the frontal pole cortex contains autoassociation attractor networks that are normally stable in a short-term memory state, and maintain stability in the other prefrontal networks during stable exploitation of goals and strategies. However, if an input from the orbitofrontal or anterior cingulate cortex that expected reward, non-reward, or punishment is received, this destabilizes the frontal pole and thereby other prefrontal networks to enable exploration of competing alternative goals and strategies. The frontal pole connectivity with reward systems may be key in exploit versus explore.

Pattern of ventral temporal lobe interconnections in rhesus macaques

The entorhinal cortex (EC, A28) is linked through reciprocal pathways with nearby perirhinal and visual, auditory, and multimodal association cortices in the temporal lobe, in pathways associated with the flow of information for memory processing. The density and laminar organization of these pathways is not well understood in primates. We studied interconnections within the ventral temporal lobe in young adult rhesus monkeys of both sexes with the aid of neural tracers injected in temporal areas (Ts1, Ts2, TE1, area 36, temporal polar area TPro, and area 28) to determine the density and laminar distribution of projection neurons within the temporal lobe. These temporal areas can be categorized into three different cortical types based on their laminar architecture: the sensory association areas Ts1, Ts2, and TE1 have six layers (eulaminate); the perirhinal limbic areas TPro and area 36 have an incipient layer IV (dysgranular); and area 28 lacks layer IV (agranular). We found that (1) temporal areas that are similar in laminar architecture by cortical type are strongly interconnected, and (2) the laminar pattern of connections is dependent on the difference in cortical laminar structure between linked areas. Thus, agranular A28 is more strongly connected with other agranular/dysgranular areas than with eulaminate cortices. Further, A28 predominantly projected via feedback-like pathways that originated in the deep layers, and received feedforward-like projections from areas of greater laminar differentiation, which emanated from the upper layers. Our results are consistent with the Structural Model, which relates the density and laminar distribution of connections to the relationship of the laminar structure between the linked areas. These connections were viewed in the context of the inhibitory microenvironment of A28, which is the key recipient of pathways from the cortex and of the output of hippocampus. Our findings revealed a higher population of calretinin (CR)-expressing neurons in EC, with a significantly higher density in its lateral division. Medial EC had a higher density of CR neurons in the deep layers, particularly in layer Va. In contrast, parvalbumin (PV) neurons were more densely distributed in the deep layers of the lateral subdivisions of rostral EC, especially in layer Va, whereas the densities of calbindin (CB) neurons in the medial and lateral EC were comparable in all layers, except for layer IIIa, in which medial EC had a higher CB population than the lateral. The pattern of connections in the inhibitory microenvironment of EC, which sends and receives input from the hippocampus, may shed light on signal propagation in this network associated with diverse aspects of memory, and disruptions in neurologic and psychiatric diseases that affect this region.

Functional ultrasound reveals effects of MRI acoustic noise on brain function

Loud acoustic noise from the scanner during functional magnetic resonance imaging (fMRI) can affect functional connectivity (FC) observed in the resting state, but the exact effect of the MRI acoustic noise on resting state FC is not well understood. Functional ultrasound (fUS) is a neuroimaging method that visualizes brain activity based on relative cerebral blood volume (rCBV), a similar neurovascular coupling response to that measured by fMRI, but without the audible acoustic noise. In this study, we investigated the effects of different acoustic noise levels (silent, 80 dB, and 110 dB) on FC by measuring resting state fUS (rsfUS) in awake mice in an environment similar to fMRI measurement. Then, we compared the results to those of resting state fMRI (rsfMRI) conducted using an 11.7 Tesla scanner. RsfUS experiments revealed a significant reduction in FC between the retrosplenial dysgranular and auditory cortexes (0.56 ± 0.07 at silence vs 0.05 ± 0.05 at 110 dB, p=.01) and a significant increase in FC anticorrelation between the infralimbic and motor cortexes (-0.21 ± 0.08 at silence vs -0.47 ± 0.04 at 110 dB, p=.017) as acoustic noise increased from silence to 80 dB and 110 dB, with increased consistency of FC patterns between rsfUS and rsfMRI being found with the louder noise conditions. Event-related auditory stimulation experiments using fUS showed strong positive rCBV changes (16.5% ± 2.9% at 110 dB) in the auditory cortex, and negative rCBV changes (-6.7% ± 0.8% at 110 dB) in the motor cortex, both being constituents of the brain network that was altered by the presence of acoustic noise in the resting state experiments. Anticorrelation between constituent brain regions of the default mode network (such as the infralimbic cortex) and those of task-positive sensorimotor networks (such as the motor cortex) is known to be an important feature of brain network antagonism, and has been studied as a biological marker of brain disfunction and disease. This study suggests that attention should be paid to the acoustic noise level when using rsfMRI to evaluate the anticorrelation between the default mode network and task-positive sensorimotor network.

Multisensory interactions of face and vocal information during perception and memory in ventrolateral prefrontal cortex

The ventral frontal lobe is a critical node in the circuit that underlies communication, a multisensory process where sensory features of faces and vocalizations come together. The neural basis of face and vocal integration is a topic of great importance since the integration of multiple sensory signals is essential for the decisions that govern our social interactions. Investigations have shown that the macaque ventrolateral prefrontal cortex (VLPFC), a proposed homologue of the human inferior frontal gyrus, is involved in the processing, integration and remembering of audiovisual signals. Single neurons in VLPFC encode and integrate species-specific faces and corresponding vocalizations. During working memory, VLPFC neurons maintain face and vocal information online and exhibit selective activity for face and vocal stimuli. Population analyses indicate that identity, a critical feature of social stimuli, is encoded by VLPFC neurons and dictates the structure of dynamic population activity in the VLPFC during the perception of vocalizations and their corresponding facial expressions. These studies suggest that VLPFC may play a primary role in integrating face and vocal stimuli with contextual information, in order to support decision making during social communication. This article is part of the theme issue 'Decision and control processes in multisensory perception'.

Cytoarchitectonic, receptor distribution and functional connectivity analyses of the macaque frontal lobe

Based on quantitative cyto- and receptor architectonic analyses, we identified 35 prefrontal areas, including novel subdivisions of Walker's areas 10, 9, 8B, and 46. Statistical analysis of receptor densities revealed regional differences in lateral and ventrolateral prefrontal cortex. Indeed, structural and functional organization of subdivisions encompassing areas 46 and 12 demonstrated significant differences in the interareal levels of α2 receptors. Furthermore, multivariate analysis included receptor fingerprints of previously identified 16 motor areas in the same macaque brains and revealed 5 clusters encompassing frontal lobe areas. We used the MRI datasets from the non-human primate data sharing consortium PRIME-DE to perform functional connectivity analyses using the resulting frontal maps as seed regions. In general, rostrally located frontal areas were characterized by bigger fingerprints, that is, higher receptor densities, and stronger regional interconnections. Whereas more caudal areas had smaller fingerprints, but showed a widespread connectivity pattern with distant cortical regions. Taken together, this study provides a comprehensive insight into the molecular structure underlying the functional organization of the cortex and, thus, reconcile the discrepancies between the structural and functional hierarchical organization of the primate frontal lobe. Finally, our data are publicly available via the EBRAINS and BALSA repositories for the entire scientific community.

What Does the Frontopolar Cortex Contribute to Goal-Directed Cognition and Action?

Understanding the unique functions of different subregions of primate prefrontal cortex has been a longstanding goal in cognitive neuroscience. Yet, the anatomy and function of one of its largest subregions (the frontopolar cortex) remain enigmatic and underspecified. Our Society for Neuroscience minisymposium Primate Frontopolar Cortex: From Circuits to Complex Behaviors will comprise a range of new anatomic and functional approaches that have helped to clarify the basic circuit anatomy of the frontal pole, its functional involvement during performance of cognitively demanding behavioral paradigms in monkeys and humans, and its clinical potential as a target for noninvasive brain stimulation in patients with brain disorders. This review consolidates knowledge about the anatomy and connectivity of frontopolar cortex and provides an integrative summary of its function in primates. We aim to answer the question: what, if anything, does frontopolar cortex contribute to goal-directed cognition and action?

Auditory verbal hallucination can be evoked by prefrontal epileptic seizure

Auditory verbal hallucinations (AVHs) have been reported in neocortical temporal epileptic seizures and have been considered highly associated with implication of auditory cortex by epileptic discharges or electrical stimulation. Herein, we report two rare frontal epilepsy cases in which AVHs featured the habitual seizures. The epileptogenic zones of these two patients were localized in the dorsal and orbitomedial prefrontal cortex, respectively by stereoelectroencephalography (SEEG) monitoring. Comparing with the AVHs in schizophrenia, we postulated that the phenomenological similarities between the two sets of AVHs imply homology in mechanisms. Ictal SEEG confirmed that the wide involvement of prefrontal-cingulate-auditory cortical network by low-voltage fast activity corresponded the occurrence with AVHs during frontal epileptic seizures. Electrical stimulation study of one of the two cases highlighted the causal role of prefrontal-cingulate cortex in the emergence of AVHs. Based on our clinical observation, SEEG findings, and electrical cortical stimulation, we supposed that wide implication of prefrontal-cingulate-auditory cortical network during epileptic seizure underlie the emergence of AVHs, and further hypothesized that AVHs could be yielded by transient deficit of self-monitoring for inner speech in focal epileptic seizures.

Local similarity of activity patterns during auditory and visual processing

Neuroimaging studies have shown that brain activity is variable and changes according to stimuli and the environmental context, reflecting brain coding or information representations at different processing levels. However, little is known about activity organization that reflects coding strategies. Here, we explored and compared two different coding approaches, spatial via cross-correlation and intensity-based coding using mutual information. Using two fMRI datasets and different seeds, we searched for the spatial and intensity-based similarities with the seeds in brain activity. Our results showed that, apart from the seed regions, significant regions detected by intensity-based similarity analysis differ completely from those found using cross-correlation. These findings may indicate that information shared through spatial coding differs from that transmitted via non-spatial coding processes. Our results suggest that brain coding is organized in several different ways to optimize information processing.

The marmoset as a model for investigating the neural basis of social cognition in health and disease

Social-cognitive processes facilitate the use of environmental cues to understand others, and to be understood by others. Animal models provide vital insights into the neural underpinning of social behaviours. To understand social cognition at even deeper behavioural, cognitive, neural, and molecular levels, we need to develop more representative study models, which allow testing of novel hypotheses using human-relevant cognitive tasks. Due to their cooperative breeding system and relatively small size, common marmosets (Callithrix jacchus) offer a promising translational model for such endeavours. In addition to having social behavioural patterns and group dynamics analogous to those of humans, marmosets have cortical brain areas relevant for the mechanistic analysis of human social cognition, albeit in simplified form. Thus, they are likely suitable animal models for deciphering the physiological processes, connectivity and molecular mechanisms supporting advanced cognitive functions. Here, we review findings emerging from marmoset social and behavioural studies, which have already provided significant insights into executive, motivational, social, and emotional dysfunction associated with neurological and psychiatric disorders.

Hearing Loss Increases Inhibitory Effects of Prefrontal Cortex Stimulation on Sound Evoked Activity in Medial Geniculate Nucleus

Sensory gating is the process whereby irrelevant sensory stimuli are inhibited on their way to higher cortical areas, allowing for focus on salient information. Sensory gating circuitry includes the thalamus as well as several cortical regions including the prefrontal cortex (PFC). Defective sensory gating has been implicated in a range of neurological disorders, including tinnitus, a phantom auditory perception strongly associated with cochlear trauma. Recently, we have shown in rats that functional connectivity between PFC and auditory thalamus, i.e., the medial geniculate nucleus (MGN), changes following cochlear trauma, showing an increased inhibitory effect from PFC activation on the spontaneous firing rate of MGN neurons. In this study, we further investigated this phenomenon using a guinea pig model, in order to demonstrate the validity of our finding beyond a single species and extend data to include data on sound evoked responses. Effects of PFC electrical stimulation on spontaneous and sound-evoked activity of single neurons in MGN were recorded in anaesthetised guinea pigs with normal hearing or hearing loss 2 weeks after acoustic trauma. No effect, inhibition and excitation were observed following PFC stimulation. The proportions of these effects were not different in animals with normal hearing and hearing loss but the magnitude of effect was. Indeed, hearing loss significantly increased the magnitude of inhibition for sound evoked responses, but not for spontaneous activity. The findings support previous observations that PFC can modulate MGN activity and that functional changes occur within this pathway after cochlear trauma. These data suggest hearing loss can alter sensory gating which may be a contributing factor toward tinnitus development.

Reduced GABAergic neuropil and interneuron profiles in schizophrenia: Complementary analysis of disease course-related differences

BACKGROUND

GABAergic interneuron dysfunction has been implicated in the pathophysiology of schizophrenia. Expression of glutamic acid decarboxylase (GAD), a key enzyme in GABA synthesis, may also be altered. Here, we have simultaneously evaluated GAD-immunoreactive (GAD-ir) neuropil and cell profiles in schizophrenia-relevant brain regions, and analysed disease-course related differences.

METHODS

GAD65/67 immunoreactivity was quantified in specific brain regions for profiles of fibres and cell bodies of interneurons by automated digital image analysis in post-mortem brains of 16 schizophrenia patients from paranoid (n = 10) and residual (n = 6) diagnostic subgroups and 16 matched controls. Regions of interest were superior temporal gyrus (STG) layers III and V, mediodorsal (MD) and laterodorsal (LD) thalamus, and hippocampal CA1 and dentate gyrus (DG) regions.

RESULTS

A reduction in GAD-ir neuropil profiles (p < 0.001), particularly in STG layer V (p = 0.012) and MD (p = 0.001), paralleled decreased GAD-ir cell profiles (p = 0.029) in schizophrenia patients compared to controls. Paranoid schizophrenia patients had lower GAD-ir neuron cell profiles in STG layers III (p = 0.007) and V (p = 0.001), MD (p = 0.002), CA1 (p = 0.001) and DG (p = 0.043) than residual patients. There was no difference in GAD-ir neuropil profiles between paranoid and residual subgroups (p = 0.369).

CONCLUSIONS

These results support the hypothesis of GABAergic dysfunction in schizophrenia. They show a more prominent reduction of GAD-ir interneurons in paranoid versus residual patients, suggestive of more pronounced GABAergic dysfunction in the former. Fully automated analyses of histological sections represent a step towards user-independent assessment of brain structure.

Cortical representation of group social communication in bats

Social interactions occur in group settings and are mediated by communication signals that are exchanged between individuals, often using vocalizations. The neural representation of group social communication remains largely unexplored. We conducted simultaneous wireless electrophysiological recordings from the frontal cortices of groups of Egyptian fruit bats engaged in both spontaneous and task-induced vocal interactions. We found that the activity of single neurons distinguished between vocalizations produced by self and by others, as well as among specific individuals. Coordinated neural activity among group members exhibited stable bidirectional interbrain correlation patterns specific to spontaneous communicative interactions. Tracking social and spatial arrangements within a group revealed a relationship between social preferences and intra- and interbrain activity patterns. Combined, these findings reveal a dedicated neural repertoire for group social communication within and across the brains of freely communicating groups of bats.

Is the prefrontal cortex organized by supramodal or modality-specific sensory demands during adolescence?

Attention is inherently biased towards the visual modality during most multisensory scenarios in adults, but the developmental trajectory towards visual dominance has not been fully elucidated. More recent evidence in primates and adult humans suggests a modality-specific stratification of the prefrontal cortex. The current study therefore used functional magnetic resonance imaging (fMRI) to investigate the neuronal correlates of proactive (following cues) and reactive (following probes) cognitive control for simultaneous audio-visual stimulation in 67 healthy adolescents (13-18 years old). Behavioral results were only partially supportive of visual dominance in adolescents, with both reduced response times and accuracy during attend-visual relative to attend-auditory trials. Differential activation of medial and lateral prefrontal cortex for processing incongruent relative to congruent stimuli (reactive control) was also only observed during attend-visual trials. There was no evidence of modality-specific prefrontal cortex stratification during the active processing of multisensory stimuli or during separate functional connectivity analyses. Attention-related modulations were also greater within visual relative to auditory cortex, but were less robust than observed in previous adult studies. Collectively, current results suggest a continued transition towards visual dominance in adolescence, as well as limited modality-specific specialization of prefrontal cortex and attentional modulations of unisensory cortex.

Is the MSB hypothesis (music as a coevolved system for social bonding) testable in the Popperian sense?

"Music As a Coevolved System for Social Bonding" (MSB) is a brilliant synthesis and appealing hypothesis offering insights into the evolution and social bonding of musicality, but is so broad and sweeping it will be challenging to test, prove or falsify in the Popperian sense (Popper, 1959). After general comments, I focus my critique on underlying neurobiological mechanisms, and offer some suggestions for experimental tests of MSB.

The cortical organization of listening effort: New insight from functional near-infrared spectroscopy

Everyday challenges impact our ability to hear and comprehend spoken language with ease, such as accented speech (source factors), spectral degradation (transmission factors), complex or unfamiliar language use (message factors), and predictability (context factors). Auditory degradation and linguistic complexity in the brain and behavior have been well investigated, and several computational models have emerged. The work here provides a novel test of the hypotheses that listening effort is partially reliant on higher cognitive auditory attention and working memory mechanisms in the frontal lobe, and partially reliant on hierarchical linguistic computation in the brain's left hemisphere. We specifically hypothesize that these models are robust and can be applied in ecologically relevant and coarse-grain contexts that rigorously control for acoustic and linguistic listening challenges. Using functional near-infrared spectroscopy during an auditory plausibility judgment task, we show the hierarchical cortical organization for listening effort in the frontal and left temporal-parietal brain regions. In response to increasing levels of cognitive demand, we found (i) poorer comprehension, (ii) slower reaction times, (iii) increasing levels of perceived mental effort, (iv) increasing levels of brain activity in the prefrontal cortex, (v) hierarchical modulation of core language processing regions that reflect increasingly higher-order auditory-linguistic processing, and (vi) a correlation between participants' mental effort ratings and their performance on the task. Our results demonstrate that listening effort is partly reliant on higher cognitive auditory attention and working memory mechanisms in the frontal lobe and partly reliant on hierarchical linguistic computation in the brain's left hemisphere. Further, listening effort is driven by a voluntary, motivation-based attention system for which our results validate the use of a single-item post-task questionnaire for measuring perceived levels of mental effort and predicting listening performance. We anticipate our study to be a starting point for more sophisticated models of listening effort and even cognitive neuroplasticity in hearing aid and cochlear implant users.

The thalamus and tinnitus: Bridging the gap between animal data and findings in humans

The neuronal mechanisms underlying tinnitus are yet to be revealed. Tinnitus, an auditory phantom sensation, used to be approached as a purely auditory domain symptom. More recently, the modulatory impact of non-auditory brain regions on the percept and burden of tinnitus are explored. The thalamus is uniquely situated to facilitate the communication between auditory and non-auditory subcortical and cortical structures. Traditionally, animal models of tinnitus have focussed on subcortical auditory structures, and research with human participants has been concerned with cortical activity in auditory and non-auditory areas. Recently, both research fields have investigated the connectivity between subcortical and cortical regions and between auditory and non-auditory areas. We show that even though the different fields employ different methods to investigate the activity and connectivity of brain areas, there is consistency in the results on tinnitus between these different approaches. This consistency between human and animals research is observed for tinnitus with peripherally instigated hearing damage, and for results obtained with salicylate and noise-induced tinnitus. The thalamus integrates input from limbic and prefrontal areas and modulates auditory activity via its connections to both subcortical and cortical auditory areas. Reported altered activity and connectivity of the auditory, prefrontal, and limbic regions suggest a more systemic approach is necessary to understand the origins and impact of tinnitus.

MRI-based Parcellation and Morphometry of the Individual Rhesus Monkey Brain: the macaque Harvard-Oxford Atlas (mHOA), a translational system referencing a standardized ontology

Investigations of the rhesus monkey (Macaca mulatta) brain have shed light on the function and organization of the primate brain at a scale and resolution not yet possible in humans. A cornerstone of the linkage between non-human primate and human studies of the brain is magnetic resonance imaging, which allows for an association to be made between the detailed structural and physiological analysis of the non-human primate and that of the human brain. To further this end, we present a novel parcellation method and system for the rhesus monkey brain, referred to as the macaque Harvard-Oxford Atlas (mHOA), which is based on the human Harvard-Oxford Atlas (HOA) and grounded in an ontological and taxonomic framework. Consistent anatomical features were used to delimit and parcellate brain regions in the macaque, which were then categorized according to functional systems. This system of parcellation will be expanded with advances in technology and, like the HOA, will provide a framework upon which the results from other experimental studies (e.g., functional magnetic resonance imaging (fMRI), physiology, connectivity, graph theory) can be interpreted.

Speech-evoked brain activity is more robust to competing speech when it is spoken by someone familiar

When speech is masked by competing sound, people are better at understanding what is said if the talker is familiar compared to unfamiliar. The benefit is robust, but how does processing of familiar voices facilitate intelligibility? We combined high-resolution fMRI with representational similarity analysis to quantify the difference in distributed activity between clear and masked speech. We demonstrate that brain representations of spoken sentences are less affected by a competing sentence when they are spoken by a friend or partner than by someone unfamiliar-effectively, showing a cortical signal-to-noise ratio (SNR) enhancement for familiar voices. This effect correlated with the familiar-voice intelligibility benefit. We functionally parcellated auditory cortex, and found that the most prominent familiar-voice advantage was manifest along the posterior superior and middle temporal gyri. Overall, our results demonstrate that experience-driven improvements in intelligibility are associated with enhanced multivariate pattern activity in posterior temporal cortex.

Categorizing human vocal signals depends on an integrated auditory-frontal cortical network

Voice signals are relevant for auditory communication and suggested to be processed in dedicated auditory cortex (AC) regions. While recent reports highlighted an additional role of the inferior frontal cortex (IFC), a detailed description of the integrated functioning of the AC-IFC network and its task relevance for voice processing is missing. Using neuroimaging, we tested sound categorization while human participants either focused on the higher-order vocal-sound dimension (voice task) or feature-based intensity dimension (loudness task) while listening to the same sound material. We found differential involvements of the AC and IFC depending on the task performed and whether the voice dimension was of task relevance or not. First, when comparing neural vocal-sound processing of our task-based with previously reported passive listening designs we observed highly similar cortical activations in the AC and IFC. Second, during task-based vocal-sound processing we observed voice-sensitive responses in the AC and IFC whereas intensity processing was restricted to distinct AC regions. Third, the IFC flexibly adapted to the vocal-sounds' task relevance, being only active when the voice dimension was task relevant. Forth and finally, connectivity modeling revealed that vocal signals independent of their task relevance provided significant input to bilateral AC. However, only when attention was on the voice dimension, we found significant modulations of auditory-frontal connections. Our findings suggest an integrated auditory-frontal network to be essential for behaviorally relevant vocal-sounds processing. The IFC seems to be an important hub of the extended voice network when representing higher-order vocal objects and guiding goal-directed behavior.

Laminar Profile of Auditory Steady-State Response in the Auditory Cortex of Awake Mice

Objective

Auditory steady-state response (ASSR) is a gamma oscillation evoked by periodic auditory stimuli, which is commonly used in clinical electroencephalographic examination to evaluate the neurological functions. Though it has been suggested that auditory cortex is the origin of ASSR, how the laminar architecture of the neocortex contributes to the ASSR recorded from the brain surface remains unclear.

Methods

We used a 16-channel silicon probe to record the local field potential and the single-unit spike activity in the different layers of the auditory cortex of unanesthetized mice. Click-trains with a repetition rate at 40-Hz were present as sound stimuli to evoke ASSR.

Results

We found that the LFPs of all cortical layers showed a stable ASSR synchronizing to the 40-Hz click stimuli, while the ASSR was strongest in the granular (thalamorecipient) layer. Furthermore, time-frequency analyses also revealed the strongest coherence between the signals recorded from the granular layer and pial surface.

Conclusion

Our results reveal that the 40-Hz ASSR primarily shows the evoked gamma oscillation of thalamorecipient layers in the neocortex, and that the ASSR may be a biomarker to detect the cognitive deficits associated with impaired thalamo-cortical connection.

Serial Prefrontal Pathways Are Positioned to Balance Cognition and Emotion in Primates

The delicate balance among primate prefrontal networks is necessary for homeostasis and behavioral flexibility. Dorsolateral prefrontal cortex (dlPFC) is associated with cognition, while the most ventromedial subgenual cingulate area 25 (A25) is associated with emotion and emotional expression. Yet A25 is weakly connected with dlPFC, and it is unknown how the two regions communicate. In rhesus monkeys of both sexes, we investigated how these functionally distinct areas may interact through pregenual anterior cingulate area 32 (A32), which is strongly connected with both. We found that dlPFC innervated the deep layers of A32, while A32 innervated all layers of A25, mostly targeting spines of excitatory neurons. Approximately 20% of A32 terminations formed synapses on inhibitory neurons in A25, notably the powerful parvalbumin inhibitory neurons in the deep layers, and the disinhibitory calretinin neurons in the superficial layers. By innervating distinct inhibitory microenvironments in laminar compartments, A32 is positioned to tune activity in columns of A25. The circuitry of the sequential pathway indicates that when dlPFC is engaged, A32 can dampen A25 output through the parvalbumin inhibitory microsystem in the deep layers of A25. A32 thus may flexibly recruit or reduce activity in A25 to maintain emotional equilibrium, a process that is disrupted in depression. Moreover, pyramidal neurons in A25 had a heightened density of NMDARs, which are the targets of novel rapid-acting antidepressants. Pharmacologic antagonism of NMDARs in patients with depression may reduce excitability in A25, mimicking the effects of the neurotypical serial pathway identified here.SIGNIFICANCE STATEMENT The anterior cingulate is a critical hub in prefrontal networks through connections with functionally distinct areas. Dorsolateral and polar prefrontal areas that are associated with complex cognition are connected with the anterior cingulate in a pattern that allows them to indirectly control downstream activity from the anterior cingulate to the subgenual cingulate, which is associated with heightened activity and negative affect in depression. This set of pathways provides a circuit mechanism for emotional regulation, with the anterior cingulate playing a balancing role for integration of cognitive and emotional processes. Disruption of these pathways may perturb network function and the ability to regulate cognitive and affective processes based on context.

Pitch Processing Can Indicate Cognitive Alterations in Chronic Liver Disease: An fNIRS Study

Early detection and evaluation of cognitive alteration in chronic liver disease is important for predicting the subsequent development of hepatic encephalopathy. While visuomotor tasks have been rigorously employed for cognitive evaluation in chronic liver disease, there is a paucity of auditory processing task. Here we focused on auditory perception and examined behavioral and haemodynamic responses to a melodic contour identification task (CIT) to compare cognitive abilities in patients with chronic liver disease (CLD, N = 30) and healthy controls (N = 25). Further, we used support vector machines to examine the optimal combination of channels of functional near-infrared spectroscopy that can classify cognitive alterations in CLD. Behavioral findings showed that CIT performance was significantly worse in the patient group and CIT significantly correlated with neurocognitive evaluation (i.e., number connection test, digit span test). The findings indicated that CIT can measure auditory cognitive capacity and its difference existing between patient group and healthy controls. Additionally, optimal subsets classified the 16-dimensional haemodynamic data with 78.35% classification accuracy, yielding markers of cognitive alterations in the prefrontal regions (CH6, CH7, CH10, CH13, CH14, and CH16). The results confirmed the potential use of behavioral as well as haemodynamic responses to music perception as an alternative or supplementary method for evaluating cognitive alterations in chronic liver disease.

Phase-amplitude coupling profiles differ in frontal and auditory cortices of bats

Neural oscillations are at the core of important computations in the mammalian brain. Interactions between oscillatory activities in different frequency bands, such as delta (1-4 Hz), theta (4-8 Hz) or gamma (>30 Hz), are a powerful mechanism for binding fundamentally distinct spatiotemporal scales of neural processing. Phase-amplitude coupling (PAC) is one such plausible and well-described interaction, but much is yet to be uncovered regarding how PAC dynamics contribute to sensory representations. In particular, although PAC appears to have a major role in audition, the characteristics of coupling profiles in sensory and integration (i.e. frontal) cortical areas remain obscure. Here, we address this question by studying PAC dynamics in the frontal-auditory field (FAF; an auditory area in the bat frontal cortex) and the auditory cortex (AC) of the bat Carollia perspicillata. By means of simultaneous electrophysiological recordings in frontal and auditory cortices examining local-field potentials (LFPs), we show that the amplitude of gamma-band activity couples with the phase of low-frequency LFPs in both structures. Our results demonstrate that the coupling in FAF occurs most prominently in delta/high-gamma frequencies (1-4/75-100 Hz), whereas in the AC the coupling is strongest in the delta-theta/low-gamma (2-8/25-55 Hz) range. We argue that distinct PAC profiles may represent different mechanisms for neuronal processing in frontal and auditory cortices, and might complement oscillatory interactions for sensory processing in the frontal-auditory cortex network.

Cortical Afferents of Area 10 in Cebus Monkeys: Implications for the Evolution of the Frontal Pole

Area 10, located in the frontal pole, is a unique specialization of the primate cortex. We studied the cortical connections of area 10 in the New World Cebus monkey, using injections of retrograde tracers in different parts of this area. We found that injections throughout area 10 labeled neurons in a consistent set of areas in the dorsolateral, ventrolateral, orbital, and medial parts of the frontal cortex, superior temporal association cortex, and posterior cingulate/retrosplenial region. However, sites on the midline surface of area 10 received more substantial projections from the temporal lobe, including clear auditory connections, whereas those in more lateral parts received >90% of their afferents from other frontal areas. This difference in anatomical connectivity reflects functional connectivity findings in the human brain. The pattern of connections in Cebus is very similar to that observed in the Old World macaque monkey, despite >40 million years of evolutionary separation, but lacks some of the connections reported in the more closely related but smaller marmoset monkey. These findings suggest that the clearer segregation observed in the human frontal pole reflects regional differences already present in early simian primates, and that overall brain mass influences the pattern of cortico-cortical connectivity.

Fronto-Temporal Coupling Dynamics During Spontaneous Activity and Auditory Processing in the Bat Carollia perspicillata

Most mammals rely on the extraction of acoustic information from the environment in order to survive. However, the mechanisms that support sound representation in auditory neural networks involving sensory and association brain areas remain underexplored. In this study, we address the functional connectivity between an auditory region in frontal cortex (the frontal auditory field, FAF) and the auditory cortex (AC) in the bat Carollia perspicillata. The AC is a classic sensory area central for the processing of acoustic information. On the other hand, the FAF belongs to the frontal lobe, a brain region involved in the integration of sensory inputs, modulation of cognitive states, and in the coordination of behavioral outputs. The FAF-AC network was examined in terms of oscillatory coherence (local-field potentials, LFPs), and within an information theoretical framework linking FAF and AC spiking activity. We show that in the absence of acoustic stimulation, simultaneously recorded LFPs from FAF and AC are coherent in low frequencies (1-12 Hz). This "default" coupling was strongest in deep AC layers and was unaltered by acoustic stimulation. However, presenting auditory stimuli did trigger the emergence of coherent auditory-evoked gamma-band activity (>25 Hz) between the FAF and AC. In terms of spiking, our results suggest that FAF and AC engage in distinct coding strategies for representing artificial and natural sounds. Taken together, our findings shed light onto the neuronal coding strategies and functional coupling mechanisms that enable sound representation at the network level in the mammalian brain.

Neural Correlates of Vocal Pitch Compensation in Individuals Who Stutter

Stuttering is a disorder that impacts the smooth flow of speech production and is associated with a deficit in sensorimotor integration. In a previous experiment, individuals who stutter were able to vocally compensate for pitch shifts in their auditory feedback, but they exhibited more variability in the timing of their corrective responses. In the current study, we focused on the neural correlates of the task using functional MRI. Participants produced a vowel sound in the scanner while hearing their own voice in real time through headphones. On some trials, the audio was shifted up or down in pitch, eliciting a corrective vocal response. Contrasting pitch-shifted vs. unshifted trials revealed bilateral superior temporal activation over all the participants. However, the groups differed in the activation of middle temporal gyrus and superior frontal gyrus [Brodmann area 10 (BA 10)], with individuals who stutter displaying deactivation while controls displayed activation. In addition to the standard univariate general linear modeling approach, we employed a data-driven technique (independent component analysis, or ICA) to separate task activity into functional networks. Among the networks most correlated with the experimental time course, there was a combined auditory-motor network in controls, but the two networks remained separable for individuals who stuttered. The decoupling of these networks may account for temporal variability in pitch compensation reported in our previous work, and supports the idea that neural network coherence is disturbed in the stuttering brain.

Essential Amino Acids, Vitamins, and Minerals Moderate the Relationship between the Right Frontal Pole and Measures of Memory

SCOPE

Nutrition has increasingly been recognized for its ability to help prevent and protect against disease, inspiring new programs of research that translate findings from nutritional science into innovative assessment tools, technologies, and therapies to advance the practice of modern medicine. A central aim in this effort is to discover specific dietary patterns that promote healthy brain aging and moderate the engagement of neural systems known to facilitate cognitive performance in later life.

METHODS AND RESULTS

The present study therefore investigates estimates of nutrient intake derived from food frequency questionnaires, structural measures of brain volume via high-resolution magnetic resonance imaging, and standardized neuropsychological measures of memory performance in nondemented elders (n = 111) using a moderation analysis. The results reveal that the essential amino acids, vitamins, and minerals nutrient pattern moderates the positive relationship between the volume of the right frontal pole and measures of both delayed and auditory memory.

CONCLUSIONS

Our findings demonstrate that a nutrient pattern including macro- and micronutrients moderate the effect of brain structure on cognitive function in old age and support the efficacy of interdisciplinary methods in nutritional cognitive neuroscience for the study of healthy brain aging.

Action perception and motor imagery: Mental practice of action

Motor cognition is related to the planning and generation of actions as well as to the recognition and imagination of motor acts. Recently, there is evidence that the motor system participates not only in overt actions but also in mental processes supporting covert actions. Within this framework, we have investigated the cortical areas engaged in execution, observation, and imagination of the same action, by the use of the high resolution quantitative ¹⁴C-deoxyglucose method in monkeys and by fMRI in humans, throughout the entire primate brain. Our data demonstrated that observing or imagining an action excites virtually the same sensory-motor cortical network which supports execution of that same action. In general agreement with the results of five relevant meta-analyses that we discuss extensively, our results imply mental practice, i.e. internal rehearsal of the action including movements and their sensory effects. We suggest that we actively perceive and imagine actions by selecting and running off-line restored sensory-motor memories, by mentally simulating the actions. We provide empirical evidence that mental simulation of actions underlies motor cognition, and conceptual representations are grounded in sensory-motor codes. Motor cognition may, therefore, be embodied and modal. Finally, we consider questions regarding agency attribution and the possible causal or epiphenomenal role the involved sensory-motor network could play in motor cognition.

Laminar profile of task-related plasticity in ferret primary auditory cortex

Rapid task-related plasticity is a neural correlate of selective attention in primary auditory cortex (A1). Top-down feedback from higher-order cortex may drive task-related plasticity in A1, characterized by enhanced neural representation of behaviorally meaningful sounds during auditory task performance. Since intracortical connectivity is greater within A1 layers 2/3 (L2/3) than in layers 4–6 (L4–6), we hypothesized that enhanced representation of behaviorally meaningful sounds might be greater in A1 L2/3 than L4–6. To test this hypothesis and study the laminar profile of task-related plasticity, we trained 2 ferrets to detect pure tones while we recorded laminar activity across a 1.8 mm depth in A1. In each experiment we analyzed high-gamma local field potentials (LFPs) and multi-unit spiking in response to identical acoustic stimuli during both passive listening and active task performance. We found that neural responses to auditory targets were enhanced during task performance, and target enhancement was greater in L2/3 than in L4–6. Spectrotemporal receptive fields (STRFs) computed from both high-gamma LFPs and multi-unit spiking showed similar increases in auditory target selectivity, also greatest in L2/3. Our results suggest that activity within intracortical networks plays a key role in the underlying neural mechanisms of selective attention.

Pathway mechanism for excitatory and inhibitory control in working memory

Humans engage in many daily activities that rely on working memory, the ability to hold and sequence information temporarily to accomplish a task. We focus on the process of working memory, based on circuit mechanisms for attending to relevant signals and suppressing irrelevant stimuli. We discuss that connections critically depend on the systematic variation in laminar structure across all cortical systems. Laminar structure is used to group areas into types regardless of their placement in the cortex, ranging from low-type agranular areas that lack layer IV to high-type areas that have six well-delineated layers. Connections vary in laminar distribution and strength based on the difference in type between linked areas, according to the "structural model" (Barbas H, Rempel-Clower N. Cereb Cortex 7: 635-646, 1997). The many possible pathways thus vary systematically by laminar distribution and strength, and they interface with excitatory neurons to select relevant stimuli and with functionally distinct inhibitory neurons that suppress activity at the site of termination. Using prefrontal pathways, we discuss how systematic architectonic variation gives rise to diverse pathways that can be recruited, along with amygdalar and hippocampal pathways that provide sensory, affective, and contextual information. The prefrontal cortex is also connected with thalamic nuclei that receive the output of the basal ganglia and cerebellum, which may facilitate fast sequencing of information. The complement of connections and their interface with distinct inhibitory neurons allows dynamic recruitment of areas and shifts in cortical rhythms to meet rapidly changing demands of sequential components of working memory tasks.

The Role of the Prefrontal Cortex in Action Perception

In an attempt to shed light on the role of the prefrontal cortex in action perception, we used the quantitative 14C-deoxyglucose method to reveal the effects elicited by reaching-to-grasp in the light or in the dark and by observation of the same action executed by an external agent. We analyzed the cortical areas in the principal sulcus, the superior and inferior lateral prefrontal convexities and the orbitofrontal cortex of monkeys. We found that execution in the light and observation activated in common most of the lateral prefrontal and orbitofrontal cortical areas, with the exception of 9/46-dorsal activated exclusively for observation and 9/46-ventral, 11 and 13 activated only for execution. Execution in the dark implicated only the ventral bank of the principal sulcus and its adjacent inferior convexity along with areas 47/12-dorsal and 13, whereas execution in the light activated both banks of the principal sulcus and both superior and inferior convexities along with areas 10 and 11. Our results demonstrate that the prefrontal cortex integrates information in the service of both action generation and action perception, and are discussed in relation to its contribution in movement suppression during action observation and in attribution of action to the correct agent.

Mixed selectivity encoding and action selection in the prefrontal cortex during threat assessment

The medial prefrontal cortex (mPFC) regulates expression of emotional behavior. The mPFC combines multivariate information from its inputs, and depending on the imminence of threat, activates downstream networks that either increase or decrease the expression of anxiety-related motor behavior and autonomic activation. Here, we selectively highlight how subcortical input to the mPFC from two example structures, the amygdala and ventral hippocampus, help shape mixed selectivity encoding and action selection during emotional processing. We outline a model where prefrontal subregions modulate behavior along orthogonal motor dimensions, and exhibit connectivity that selects for expression of one behavioral strategy while inhibiting the other.

Parallel trends in cortical gray and white matter architecture and connections in primates allow fine study of pathways in humans and reveal network disruptions in autism

Noninvasive imaging and tractography methods have yielded information on broad communication networks but lack resolution to delineate intralaminar cortical and subcortical pathways in humans. An important unanswered question is whether we can use the wealth of precise information on pathways from monkeys to understand connections in humans. We addressed this question within a theoretical framework of systematic cortical variation and used identical high-resolution methods to compare the architecture of cortical gray matter and the white matter beneath, which gives rise to short- and long-distance pathways in humans and rhesus monkeys. We used the prefrontal cortex as a model system because of its key role in attention, emotions, and executive function, which are processes often affected in brain diseases. We found striking parallels and consistent trends in the gray and white matter architecture in humans and monkeys and between the architecture and actual connections mapped with neural tracers in rhesus monkeys and, by extension, in humans. Using the novel architectonic portrait as a base, we found significant changes in pathways between nearby prefrontal and distant areas in autism. Our findings reveal that a theoretical framework allows study of normal neural communication in humans at high resolution and specific disruptions in diverse psychiatric and neurodegenerative diseases.

Cortical Connections Position Primate Area 25 as a Keystone for Interoception, Emotion, and Memory

The structural and functional integrity of subgenual cingulate area 25 (A25) is crucial for emotional expression and equilibrium. A25 has a key role in affective networks, and its disruption has been linked to mood disorders, but its cortical connections have yet to be systematically or fully studied. Using neural tracers in rhesus monkeys, we found that A25 was densely connected with other ventromedial and posterior orbitofrontal areas associated with emotions and homeostasis. A moderate pathway linked A25 with frontopolar area 10, an area associated with complex cognition, which may regulate emotions and dampen negative affect. Beyond the frontal lobe, A25 was connected with auditory association areas and memory-related medial temporal cortices, and with the interoceptive-related anterior insula. A25 mostly targeted the superficial cortical layers of other areas, where broadly dispersed terminations comingled with modulatory inhibitory or disinhibitory microsystems, suggesting a dominant excitatory effect. The architecture and connections suggest that A25 is the consummate feedback system in the PFC. Conversely, in the entorhinal cortex, A25 pathways terminated in the middle-deep layers amid a strong local inhibitory microenvironment, suggesting gating of hippocampal output to other cortices and memory storage. The graded cortical architecture and associated laminar patterns of connections suggest how areas, layers, and functionally distinct classes of inhibitory neurons can be recruited dynamically to meet task demands. The complement of cortical connections of A25 with areas associated with memory, emotion, and somatic homeostasis provide the circuit basis to understand its vulnerability in psychiatric and neurologic disorders.SIGNIFICANCE STATEMENT Integrity of the prefrontal subgenual cingulate cortex is crucial for healthy emotional function. Subgenual area 25 (A25) is mostly linked with other prefrontal areas associated with emotion in a dense network positioned to recruit large fields of cortex. In healthy states, A25 is associated with internal states, autonomic function, and transient negative affect. Constant hyperactivity in A25 is a biomarker for depression in humans and may trigger extensive activation in its dominant connections with areas associated with emotions and internal balance. A pathway between A25 and frontopolar area 10 may provide a critical link to regulate emotions and dampen persistent negative affect, which may be explored for therapeutic intervention in depression.

Anterior Cingulate Pathways May Affect Emotions Through Orbitofrontal Cortex

The anterior cingulate cortex (ACC) and posterior orbitofrontal cortex (pOFC) are associated with emotional regulation. These regions are old in phylogeny and have widespread connections with eulaminate neocortices, intricately linking areas associated with emotion and cognition. The ACC and pOFC have distinct cortical and subcortical connections and are also interlinked, but the pattern of their connections-which may be used to infer the flow of information between them-is not well understood. Here we found that pathways from ACC area 32 innervated all pOFC areas with a significant proportion of large and efficient terminals, seen at the level of the system and the synapse. The pathway from area 32 targeted overwhelmingly elements of excitatory neurons in pOFC, with few postsynaptic sites found on presumed inhibitory neurons. Moreover, pathways from area 32 originated mostly in the upper layers and innervated preferentially the middle-deep layers of the least differentiated pOFC areas, in a pattern reminiscent of feedforward communication. Pathway terminations from area 32 overlapped in the deep layers of pOFC with output pathways that project to the thalamus and the amygdala, and may have cascading downstream effects on emotional and cognitive processes and their disruption in psychiatric disorders.

Look Hear! The Prefrontal Cortex is Stratified by Modality of Sensory Input During Multisensory Cognitive Control

Parsing multisensory information from a complex external environment is a fundamental skill for all organisms. However, different organizational schemes currently exist for how multisensory information is processed in human (supramodal; organized by cognitive demands) versus primate (organized by modality/cognitive demands) lateral prefrontal cortex (LPFC). Functional magnetic resonance imaging results from a large cohort of healthy controls (N = 64; Experiment 1) revealed a rostral-caudal stratification of LPFC for auditory versus visual attention during an audio-visual Stroop task. The stratification existed in spite of behavioral and functional evidence of increased interference from visual distractors. Increased functional connectivity was also observed between rostral LPFC and auditory cortex across independent samples (Experiments 2 and 3) and multiple methodologies. In contrast, the caudal LPFC was preferentially activated during visual attention but functioned in a supramodal capacity for resolving multisensory conflict. The caudal LPFC also did not exhibit increased connectivity with visual cortices. Collectively, these findings closely mirror previous nonhuman primate studies suggesting that visual attention relies on flexible use of a supramodal cognitive control network in caudal LPFC whereas rostral LPFC is specialized for directing attention to auditory inputs (i.e., human auditory fields).

Early cortical metabolic rearrangement related to clinical data in idiopathic sudden sensorineural hearing loss

Results in studies concerning cortical changes in idiopathic sudden sensorineural hearing loss (ISSNHL) are not homogeneous, in particular due to the different neuroimaging techniques implemented and the diverse stages of ISSNHL studied. Considering the recent advances in state-of-the-art positron emission tomography (PET) cameras, the aim of this study was to gain more insight into the neuroanatomical differences associated with the earliest stages of unilateral ISSNHL and clinical-perceptual performance changes. After an audiological examination including the mean auditory threshold (mean AT), mean speech discrimination score (mean SDS) and Tinnitus Handicap Inventory (THI), 14 right-handed ISSNHL patients underwent brain [¹⁸F]fluorodeoxyglucose (FDG)-PET within 72 h of the onset of symptoms. When compared to an homogeneous group of 35 healthy subjects by means of statistical parametric mapping, a relative increase in FDG uptake was found in the right superior and medial frontal gyrus as well as in the right anterior cingulate cortex in ISSNHL patients. Conversely, the same group showed a significant relative decrease in FDG uptake in the right middle temporal, precentral and postcentral gyrus as well as in the left posterior cingulate cortex, left lingual, superior, middle temporal and middle frontal gyrus and in the left insula. Regression analysis showed a positive correlation between mean THI and glucose consumption in the right anterior cingulate cortex and a positive correlation between mean SDS and glucose consumption in the left precentral gyrus. The relative changes in FDG uptake found in these brain regions and the positive correlation with mean SDS and THI scores in ISSNHL could possibly highlight new aspects of cerebral rearrangement, contributing to further explain changes in those functions that support speech recognition during the sudden impairment of unilateral auditory input.

Evidence for a Large-Scale Brain System Supporting Allostasis and Interoception in Humans

Large-scale intrinsic brain systems have been identified for exteroceptive senses (e.g., sight, hearing, touch). We introduce an analogous system for representing sensations from within the body, called interoception, and demonstrate its relation to regulating peripheral systems in the body, called allostasis. Employing the recently introduced Embodied Predictive Interoception Coding (EPIC) model, we used tract-tracing studies of macaque monkeys, followed by two intrinsic functional magnetic resonance imaging samples (N = 280 and N = 270) to evaluate the existence of an intrinsic allostatic/interoceptive system in the human brain. Another sample (N = 41) allowed us to evaluate the convergent validity of the hypothesized allostatic/interoceptive system by showing that individuals with stronger connectivity between system hubs performed better on an implicit index of interoceptive ability related to autonomic fluctuations. Implications include insights for the brain's functional architecture, dissolving the artificial boundary between mind and body, and unifying mental and physical illness.

Magnitude Codes for Cross-Modal Working Memory in the Primate Frontal Association Cortex

Quantitative features of stimuli may be ordered along a magnitude continuum, or line. Magnitude refers to parameters of different types of stimulus properties. For instance, the frequency of a sound relates to sensory and continuous stimulus properties, whereas the number of items in a set is an abstract and discrete property. In addition, within a stimulus property, magnitudes need to be processed not only in one modality, but across multiple modalities. In the sensory domain, for example, magnitude applies to both to the frequency of auditory sounds and tactile vibrations. Similarly, both the number of visual items and acoustic events constitute numerical quantity, or numerosity. To support goal-directed behavior and executive functions across time, magnitudes need to be held in working memory, the ability to briefly retain and manipulate information in mind. How different types of magnitudes across multiple modalities are represented in working memory by single neurons has only recently been explored in primates. These studies show that neurons in the frontal lobe can encode the same magnitude type across sensory modalities. However, while multimodal sensory magnitude in relative comparison tasks is represented by monotonically increasing or decreasing response functions ("summation code"), multimodal numerical quantity in absolute matching tasks is encoded by neurons tuned to preferred numerosities ("labeled-line code"). These findings indicate that most likely there is not a single type of cross-modal working-memory code for magnitudes, but rather a flexible code that depends on the stimulus dimension as well as on the task requirements.

GABAergic system impairment in the hippocampus and superior temporal gyrus of patients with paranoid schizophrenia: A post-mortem study

BACKGROUND

Glutamic acid decarboxylase (GAD) is a key enzyme in GABA synthesis and alterations in GABAergic neurotransmission related to glial abnormalities are thought to play a crucial role in the pathophysiology of schizophrenia. This study aimed to identify potential differences regarding the neuropil expression of GAD between paranoid and residual schizophrenia.

METHODS

GAD65/67 immunostained histological sections were evaluated by quantitative densitometric analysis of GAD-immunoreactive (ir) neuropil. Regions of interest were the hippocampal formation (CA1 field and dentate gyrus [DG]), superior temporal gyrus (STG), and laterodorsal thalamic nucleus (LD). Data from 16 post-mortem schizophrenia patient samples (10 paranoid and 6 residual schizophrenia cases) were compared with those from 16 matched controls.

RESULTS

Overall, schizophrenia patients showed a lower GAD-ir neuropil density (P=0.014), particularly in the right CA1 (P=0.033). However, the diagnostic subgroups differed significantly (P<0.001), mainly because of lower right CA1 GAD-ir neuropil density in paranoid versus residual patients (P=0.036) and controls (P<0.003). Significant GAD-ir neuropil reduction was also detected in the right STG layer V of paranoid versus residual schizophrenia cases (P=0.042). GAD-ir neuropil density correlated positively with antipsychotic dosage, particularly in CA1 (right: r=0.850, P=0.004; left: r=0.800, P=0.010).

CONCLUSION

Our finding of decreased relative density of GAD-ir neuropil suggests hypofunction of the GABAergic system, particularly in hippocampal CA1 field and STG layer V of patients with paranoid schizophrenia. The finding that antipsychotic medication seems to counterbalance GABAergic hypofunction in schizophrenia patients suggests the possibility of exploring new treatment avenues which target this system.

How the prefrontal executive got its stripes

Pathways from cortical and subcortical structures give the prefrontal cortex a panoramic view of the sensory environment and the internal milieu of motives and drives. The prefrontal cortex also receives privileged information from the output of the basal ganglia and cerebellum and innervates widely the inhibitory thalamic reticular nucleus that gates thalamo-cortical communication. Connections, in general, are strongly related to the systematic structural variation of the cortex that can be traced to development. Insights from development have profound implications for the special connections of the prefrontal cortex for executive control, learning and memory, and vulnerability in psychiatric and neurologic diseases.

Monkey׳s short-term auditory memory nearly abolished by combined removal of the rostral superior temporal gyrus and rhinal cortices

While monkeys easily acquire the rules for performing visual and tactile delayed matching-to-sample, a method for testing recognition memory, they have extraordinary difficulty acquiring a similar rule in audition. Another striking difference between the modalities is that whereas bilateral ablation of the rhinal cortex (RhC) leads to profound impairment in visual and tactile recognition, the same lesion has no detectable effect on auditory recognition memory (Fritz et al., 2005). In our previous study, a mild impairment in auditory memory was obtained following bilateral ablation of the entire medial temporal lobe (MTL), including the RhC, and an equally mild effect was observed after bilateral ablation of the auditory cortical areas in the rostral superior temporal gyrus (rSTG). In order to test the hypothesis that each of these mild impairments was due to partial disconnection of acoustic input to a common target (e.g., the ventromedial prefrontal cortex), in the current study we examined the effects of a more complete auditory disconnection of this common target by combining the removals of both the rSTG and the MTL. We found that the combined lesion led to forgetting thresholds (performance at 75% accuracy) that fell precipitously from the normal retention duration of ~30 to 40s to a duration of ~1 to 2s, thus nearly abolishing auditory recognition memory, and leaving behind only a residual echoic memory. This article is part of a Special Issue entitled SI: Auditory working memory.