Cingulate cortical cells projecting to monkey frontal eye field and primary motor cortex

Functional parcellation of the cingulate gyrus by electrical cortical stimulation: a synthetic literature review and future directions

BACKGROUND

The cingulate gyrus (CG), a brain structure above the corpus callosum, is recognised as part of the limbic system and plays numerous vital roles. However, its full functional capacity is yet to be understood. In recent years, emerging evidence from imaging modalities, supported by electrical cortical stimulation (ECS) findings, has improved our understanding. To our knowledge, there is a limited number of systematic reviews of the cingulate function studied by ECS. We aim to parcellate the CG by reviewing ECS studies.

DESIGN/METHODS

We searched PubMed and Embase for studies investigating CG using ECS. A total of 30 studies met the inclusion criteria. We evaluated the ECS responses across the cingulate subregions and summarised the reported findings.

RESULTS

We included 30 studies (totalling 887 patients, with a mean age of 31.8±9.8 years). The total number of electrodes implanted within the cingulate was 3028 electrode contacts; positive responses were obtained in 941 (31.1%, median percentages, 32.3%, IQR 22.2%-64.3%). The responses elicited from the CG were as follows. Simple motor (8 studies, 26.7 %), complex motor (10 studies, 33.3%), gelastic with and without mirth (7 studies, 23.3%), somatosensory (9 studies, 30%), autonomic (11 studies, 36.7 %), psychic (8 studies, 26.7%) and vestibular (3 studies, 10%). Visual and speech responses were also reported. Despite some overlap, the results indicate that the anterior cingulate cortex is responsible for most emotional, laughter and autonomic responses, while the middle cingulate cortex controls most complex motor behaviours, and the posterior cingulate cortex (PCC) regulates visual, among various other responses. Consistent null responses have been observed across different regions, emphasising PCC.

CONCLUSIONS

Our results provide a segmental mapping of the functional properties of CG, helping to improve precision in the surgical planning of epilepsy.

Cingulate Cortex: Anatomy, Structural and Functional Connectivity

SUMMARY

The cingulate cortex is a paired brain region located on the medial wall of each hemisphere. This review explores the anatomy as well as the structural and functional connectivity of the cingulate cortex underlying essential roles this region plays in emotion, autonomic, cognitive, motor control, visual-spatial processing, and memory.

Quantitative comparison of corticospinal tracts arising from different cortical areas in humans

The corticospinal tract (CST), which plays a major role in the control of voluntary limb movements, arises from multiple motor- and somatosensory-related areas in monkeys. Although the cortical origin and quantitative differences in CSTs among the cortical areas are well-documented in monkeys, they are unclear in humans. We quantitatively investigated the CSTs from the cerebral cortex to the cervical cord in healthy volunteers using fiber tractography of diffusion-weighted magnetic resonance imaging. The corticospinal (CS) streamlines arose from nine cortical areas: primary motor area (mean ± SD = 49.71 ± 1.61%), dorsal (16.33 ± 1.37%) and ventral (11.02 ± 0.90%) premotor cortex, supplementary motor area (5.14 ± 0.36%), pre-supplementary motor area (2.46 ± 0.26%), primary somatosensory cortex (11.06 ± 0.91%), Brodmann area 5 (0.88 ± 0.09%), caudal cingulate zone (1.70 ± 0.30%), and posterior part of the rostral cingulate zone (1.70 ± 0.34%). In all cortical areas, the number of CS streamlines gradually decreased from the rostral to caudal spinal segments, but the proportion was maintained throughout the cervical cord. Over 75% of CS streamlines arose from the lateral surface of the frontal lobe, which may explain the voluntary control of dexterous and flexible limb movements in humans. (197/200 words).

Cortical visual area CSv as a cingulate motor area: a sensorimotor interface for the control of locomotion

The response properties, connectivity and function of the cingulate sulcus visual area (CSv) are reviewed. Cortical area CSv has been identified in both human and macaque brains. It has similar response properties and connectivity in the two species. It is situated bilaterally in the cingulate sulcus close to an established group of medial motor/premotor areas. It has strong connectivity with these areas, particularly the cingulate motor areas and the supplementary motor area, suggesting that it is involved in motor control. CSv is active during visual stimulation but only if that stimulation is indicative of self-motion. It is also active during vestibular stimulation and connectivity data suggest that it receives proprioceptive input. Connectivity with topographically organized somatosensory and motor regions strongly emphasizes the legs over the arms. Together these properties suggest that CSv provides a key interface between the sensory and motor systems in the control of locomotion. It is likely that its role involves online control and adjustment of ongoing locomotory movements, including obstacle avoidance and maintaining the intended trajectory. It is proposed that CSv is best seen as part of the cingulate motor complex. In the human case, a modification of the influential scheme of Picard and Strick (Picard and Strick, Cereb Cortex 6:342–353, 1996) is proposed to reflect this.

The cingulate oculomotor cortex

Knowledge about the relevance and extent of human eye movement control in the cingulate cortex to date is very limited. Experiments in non-human primates brought about evidence for a potentially central role of the dorsal bank of the cingulate sulcus in saccadic eye movements. In humans, a putative cingulate eye field (CEF) in the same region has been proposed; however, its function and location still remain controversial. Another area in the posterior cingulate cortex, the cingulate sulcus visual area (CSv), has been shown to respond to visual motion cues and also ocular motor tasks. In this study we used multi-band neuroimaging (n = 46) to comprehensively characterize oculomotor responses along the entire cingulate cortex during the most common types of eye movements. We were able to robustly localize the CEF to the anterior portion of the midcingulate gyrus. The region gave responses during all oculomotor tasks and is embedded within the ventral attention network. Area CSv, which is located in the anterior portion of the posterior cingulate gyrus, on the other hand responded to smooth pursuit and optokinetic nystagmus only. It likewise represents a node within the ventral attention network but at the same time seems to be a distinctive part of the somatomotor network. Our findings support an executive role of the CEF, suggesting a cognitive control function in maintaining and adapting different kinds of eye movements. CSv on the other hand might be an interface for relaying oculomotor, visual motion and broad sensory signals related to self-motion.

The posterior parietal cortex contributes to visuomotor processing for saccades in blindsight macaques

Patients with damage to the primary visual cortex (V1) lose visual awareness, yet retain the ability to perform visuomotor tasks, which is called “blindsight.” To understand the neural mechanisms underlying this residual visuomotor function, we studied a non-human primate model of blindsight with a unilateral lesion of V1 using various oculomotor tasks. Functional brain imaging by positron emission tomography showed a significant change after V1 lesion in saccade-related visuomotor activity in the intraparietal sulcus area in the ipsi- and contralesional posterior parietal cortex. Single unit recordings in the lateral bank of the intraparietal sulcus (lbIPS) showed visual responses to targets in the contralateral visual field on both hemispheres. Injection of muscimol into the ipsi- or contralesional lbIPSs significantly impaired saccades to targets in the V1 lesion-affected visual field, differently from previous reports in intact animals. These results indicate that the bilateral lbIPSs contribute to visuomotor function in blindsight.

Rikako Kato et al. use PET imaging to examine altered brain activity in blindsight macaques that lack visual awareness yet can still perform visuomotor tasks. They report that blindsight macaques exhibit a significant change in activity of the lateral bank of the intraparietal sulcus (lbIPS) bilaterally, and injection of muscimol into this region impairs visuomotor performance. These results suggest a role for the bilateral lbIPS in visuomotor function in blindsight conditions.

Functional connectivity during smooth pursuit eye movements

Smooth pursuit eye movements (SPEM) hold the image of a slowly moving stimulus on the fovea. The neural system underlying SPEM primarily includes visual, parietal, and frontal areas. In the present study, we investigated how these areas are functionally coupled and how these couplings are influenced by target motion frequency. To this end, healthy participants (n = 57) were instructed to follow a sinusoidal target stimulus moving horizontally at two different frequencies (0.2 Hz, 0.4 Hz). Eye movements and blood oxygen level-dependent (BOLD) activity were recorded simultaneously. Functional connectivity of the key areas of the SPEM network was investigated with a psychophysiological interaction (PPI) approach. How activity in five eye movement-related seed regions (lateral geniculate nucleus, V1, V5, posterior parietal cortex, frontal eye fields) relates to activity in other parts of the brain during SPEM was analyzed. The behavioral results showed clear deterioration of SPEM performance at higher target frequency. BOLD activity during SPEM versus fixation occurred in a geniculo-occipito-parieto-frontal network, replicating previous findings. PPI analysis yielded widespread, partially overlapping networks. In particular, frontal eye fields and posterior parietal cortex showed task-dependent connectivity to large parts of the entire cortex, whereas other seed regions demonstrated more regionally focused connectivity. Higher target frequency was associated with stronger activations in visual areas but had no effect on functional connectivity. In summary, the results confirm and extend previous knowledge regarding the neural mechanisms underlying SPEM and provide a valuable basis for further investigations such as in patients with SPEM impairments and known alterations in brain connectivity.NEW & NOTEWORTHY This study provides a comprehensive investigation of blood oxygen level-dependent (BOLD) functional connectivity during smooth pursuit eye movements. Results from a large sample of healthy participants suggest that key oculomotor regions interact closely with each other but also with regions not primarily associated with eye movements. Understanding functional connectivity during smooth pursuit is important, given its potential role as an endophenotype of psychoses.

Whole brain mapping of somatosensory responses in awake marmosets investigated with ultra-high-field fMRI

The common marmoset (Callithrix jacchus) is a small-bodied New World primate that is becoming an important model to study brain functions. Despite several studies exploring the somatosensory system of marmosets, all results have come from anesthetized animals using invasive techniques and postmortem analyses. Here, we demonstrate the feasibility for getting high-quality and reproducible somatosensory mapping in awake marmosets with functional magnetic resonance imaging (fMRI). We acquired fMRI sequences in four animals, while they received tactile stimulation (via air-puffs), delivered to the face, arm, or leg. We found a topographic body representation with the leg representation in the most medial part, the face representation in the most lateral part, and the arm representation between leg and face representation within areas 3a, 3b, and 1/2. A similar sequence from leg to face from caudal to rostral sites was identified in areas S2 and PV. By generating functional connectivity maps of seeds defined in the primary and second somatosensory regions, we identified two clusters of tactile representation within the posterior and midcingulate cortex. However, unlike humans and macaques, no clear somatotopic maps were observed. At the subcortical level, we found a somatotopic body representation in the thalamus and, for the first time in marmosets, in the putamen. These maps have similar organizations, as those previously found in Old World macaque monkeys and humans, suggesting that these subcortical somatotopic organizations were already established before Old and New World primates diverged. Our results show the first whole brain mapping of somatosensory responses acquired in a noninvasive way in awake marmosets.NEW & NOTEWORTHY We used somatosensory stimulation combined with functional MRI (fMRI) in awake marmosets to reveal the topographic body representation in areas S1, S2, thalamus, and putamen. We showed the existence of a body representation organization within the thalamus and the cingulate cortex by computing functional connectivity maps from seeds defined in S1/S2, using resting-state fMRI data. This noninvasive approach will be essential for chronic studies by guiding invasive recording and manipulation techniques.

Functional MRI in Macaque Monkeys during Task Switching

Nonhuman primates have proven to be a valuable animal model for exploring neuronal mechanisms of cognitive control. One important aspect of executive control is the ability to switch from one task to another, and task-switching paradigms have often been used in human volunteers to uncover the underlying neuronal processes. To date, however, no study has investigated task-switching paradigms in nonhuman primates during functional magnetic resonance imaging (fMRI). We trained two rhesus macaques to switch between arm movement, eye movement, and passive fixation tasks during fMRI. Similar to results obtained in human volunteers, task switching elicits increased fMRI activations in prefrontal cortex, anterior cingulate cortex, orbitofrontal cortex, and caudate nucleus. Our results indicate that the macaque monkey is a reliable model with which to investigate higher-order cognitive functioning such as task switching. As such, these results can pave the way for a detailed investigation of the neural basis of complex human behavior.SIGNIFICANCE STATEMENT Task switching is an important aspect of cognitive control, and task-switching paradigms have often been used to investigate higher-order executive functioning in human volunteers. We used a task-switching paradigm in the nonhuman primate during fMRI and found increased activation mainly in prefrontal areas (46, 45, frontal eye field, and anterior cingulate), in orbitofrontal area 12, and in the caudate nucleus. These data fit surprisingly well with previous human imaging data, proving that the monkey is an excellent model to study task switching with high spatiotemporal resolution tools that are currently not applicable in humans. As such, our results pave the way for a detailed interrogation of regions performing similar executive functions in humans and monkeys.

Reward activations and face fields in monkey cingulate motor areas

Several premotor areas have been identified within primate cingulate cortex; however their function is yet to be uncovered. Recent brain imaging work in humans revealed a topographic anatomofunctional overlap between feedback processing during exploratory behaviors and the corresponding body fields in the rostral cingulate motor area (RCZa), suggesting an embodied representation of feedback. In particular, a face field in RCZa processes juice feedback. Here we tested an extension of the embodied principle in which unexpected or relevant information obtained through the eye or the face would be processed by face fields in cingulate motor areas, and whether this applied to monkey cingulate cortex. We show that activations for juice reward, eye movement, eye blink, and tactile stimulation on the face overlap over two subfields within the cingulate sulcus likely corresponding to the rostral and caudal cingulate motor areas. This suggests that in monkeys as is the case in humans, behaviorally relevant information is processed through multiple cingulate body/effector maps.

NEW & NOTEWORTHY What is the role of cingulate motor areas? In this study we observed in monkeys that, as in humans, neural responses to face-related events, juice reward, eye movement, eye blink, and tactile stimulations, clustered redundantly in two separate cingulate subfields. This suggests that behaviorally relevant information is processed by multiple cingulate effector maps. Importantly, this overlap supports the principle that the cingulate cortex processes feedback based on where it is experienced on the body.

Rostro-Caudal Organization of Connectivity between Cingulate Motor Areas and Lateral Frontal Regions

According to contemporary views, the lateral frontal cortex is organized along a rostro-caudal functional axis with increasingly complex cognitive/behavioral control implemented rostrally, and increasingly detailed motor control implemented caudally. Whether the medial frontal cortex follows the same organization remains to be elucidated. To address this issue, the functional connectivity of the 3 cingulate motor areas (CMAs) in the human brain with the lateral frontal cortex was investigated. First, the CMAs and their representations of hand, tongue, and eye movements were mapped via task-related functional magnetic resonance imaging (fMRI). Second, using resting-state fMRI, their functional connectivity with lateral prefrontal and lateral motor cortical regions of interest (ROIs) were examined. Importantly, the above analyses were conducted at the single-subject level to account for variability in individual cingulate morphology. The results demonstrated a rostro-caudal functional organization of the CMAs in the human brain that parallels that in the lateral frontal cortex: the rostral CMA has stronger functional connectivity with prefrontal regions and weaker connectivity with motor regions; conversely, the more caudal CMAs have weaker prefrontal and stronger motor connectivity. Connectivity patterns of the hand, tongue and eye representations within the CMAs are consistent with that of their parent CMAs. The parallel rostral-to-caudal functional organization observed in the medial and lateral frontal cortex could likely contribute to different hierarchies of cognitive-motor control.

Frontal eye field in prosimian galagos: Intracortical microstimulation and tracing studies

The frontal eye field (FEF) in prosimian primates was identified as a small cortical region, above and anterior to the anterior frontal sulcus, from which saccadic eye movements were evoked with electrical stimulation. Tracer injections revealed FEF connections with cortical and subcortical structures participating in higher order visual processing. Ipsilateral cortical connections were the densest with adjoining parts of the dorsal premotor and prefrontal cortex (PFC). Label in a region corresponding to supplementary eye field (SEF) of other primates, suggests the existence of SEF in galagos. Other connections were with ventral premotor cortex (PMV), the caudal half of posterior parietal cortex, cingulate cortex, visual areas within the superior temporal sulcus, and inferotemporal cortex. Callosal connections were mostly with the region of the FEF of another hemisphere, SEF, PFC, and PMV. Most subcortical connections were ipsilateral, but some were bilateral. Dense bilateral connections were to caudate nuclei. Densest reciprocal ipsilateral connections were with the paralamellar portion of mediodorsal nucleus, intralaminar nuclei and magnocellular portion of ventral anterior nucleus. Other FEF connections were with the claustrum, reticular nucleus, zona incerta, lateral posterior and medial pulvinar nuclei, nucleus limitans, pretectal area, nucleus of Darkschewitsch, mesencephalic and pontine reticular formation and pontine nuclei. Surprisingly, the superior colliculus (SC) contained only sparse anterograde label. Although most FEF connections in galagos are similar to those in monkeys, the FEF-SC connections appear to be much less. This suggests that a major contribution of the FEF to visuomotor functions of SC emerged with the evolution of anthropoid primates.

Theta and beta synchrony coordinate frontal eye fields and anterior cingulate cortex during sensorimotor mapping

The frontal eye fields (FEFs) and the anterior cingulate cortex (ACC) are commonly coactivated for cognitive saccade tasks, but whether this joined activation indexes coordinated activity underlying successful guidance of sensorimotor mapping is unknown. Here we test whether ACC and FEF circuits coordinate through phase synchronization of local field potential and neural spiking activity in macaque monkeys performing memory-guided and pro- and anti-saccades. We find that FEF and ACC showed prominent synchronization at a 3–9 Hz theta and a 12–30 Hz beta frequency band during the delay and preparation periods with a strong Granger-causal influence from ACC to FEF. The strength of theta- and beta-band coherence between ACC and FEF but not variations in power predict correct task performance. Taken together, the results support a role of ACC in cognitive control of frontoparietal networks and suggest that narrow-band theta and to some extent beta rhythmic activity indexes the coordination of relevant information during periods of enhanced control demands.

Frontal eye fields (FEF) and anterior cingulate cortex (ACC) are coactivated during cognitive tasks, but the precise format of their interaction is not known. Here the authors show that phase coupling between ACC -FEF in theta and beta frequency bands better predicts behavioural performance.

Failure to mobilize cognitive control for challenging tasks correlates with symptom severity in schizophrenia

Deficits in the adaptive, flexible control of behavior contribute to the clinical manifestations of schizophrenia. We used functional MRI and an antisaccade paradigm to examine the neural correlates of cognitive control deficits and their relations to symptom severity. Thirty-three chronic medicated outpatients with schizophrenia and 31 healthy controls performed an antisaccade paradigm. We examined differences in recruitment of the cognitive control network and task performance for Hard (high control) versus Easy (low control) antisaccade trials within and between groups. We focused on the key regions involved in ‘top-down’ control of ocular motor structures – dorsal anterior cingulate cortex, dorsolateral and ventrolateral prefrontal cortex. In patients, we examined whether difficulty implementing cognitive control correlated with symptom severity. Patients made more errors overall, and had shorter saccadic latencies than controls on correct Hard vs. Easy trials. Unlike controls, patients failed to increase activation in the cognitive control network for Hard vs. Easy trials. Reduced activation for Hard vs. Easy trials predicted higher error rates in both groups and increased symptom severity in schizophrenia. These findings suggest that patients with schizophrenia are impaired in mobilizing cognitive control when presented with challenges and that this contributes to deficits suppressing prepotent but contextually inappropriate responses, to behavior that is stimulus-bound and error-prone rather than flexibly guided by context, and to symptom expression. Therapies aimed at increasing cognitive control may improve both cognitive flexibility and reduce the impact of symptoms.

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Patients with schizophrenia fail to mobilize the cognitive control network during a challenging cognitive task.

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This deficit results in behavior that is stimulus-bound and error-prone rather than flexibly guided by context.

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Therapies aimed at increasing cognitive control may improve both cognitive flexibility and reduce the impact of symptoms.

Transient Pupil Dilation after Subsaccadic Microstimulation of Primate Frontal Eye Fields

Pupillometry provides a simple and noninvasive index for a variety of cognitive processes, including perception, attention, task consolidation, learning, and memory. The neural substrates by which such cognitive processes influence pupil diameter remain somewhat unclear, although cortical inputs to the locus coeruleus mediating arousal are likely involved. Changes in pupil diameter also accompany covert orienting; hence the oculomotor system may provide an alternative substrate for cognitive influences on pupil diameter. Here, we show that low-level electrical microstimulation of the primate frontal eye fields (FEFs), a cortical component of the oculomotor system strongly connected to the intermediate layers of the superior colliculus (SCi), evoked robust pupil dilation even in the absence of evoked saccades. The magnitude of such dilation scaled with increases in stimulation parameters, depending strongly on the intensity and number of pulses. Although there are multiple pathways by which FEF stimulation could cause pupil dilation, the timing and profile of dilation closely resembled that evoked by SCi stimulation. Moreover, pupil dilation evoked from the FEFs increased when presumed oculomotor activity was higher at the time of stimulation. Our findings implicate the oculomotor system as a potential substrate for how cognitive processes can influence pupil diameter. We suggest that a pathway from the frontal cortex through the SCi operates in parallel with frontal inputs to arousal circuits to regulate task-dependent modulation of pupil diameter, perhaps indicative of an organization wherein one pathway assumes primacy for a given cognitive process.

SIGNIFICANCE STATEMENT

Pupillometry (the measurement of pupil diameter) provides a simple and noninvasive index for a variety of cognitive processes, offering a biomarker that has value in both health and disease. But how do cognitive processes influence pupil diameter? Here, we show that low-level stimulation of the primate frontal eye fields can induce robust pupil dilation without saccades. Pupil dilation scaled with the number and intensity of stimulation pulses and varied with endogenous oculomotor activity at the time of stimulation. The oculomotor system therefore provides a plausible pathway by which cognitive processes may influence pupil diameter, perhaps operating in conjunction with systems regulating arousal.

Distinct neuronal organizations of the caudal cingulate motor area and supplementary motor area in monkeys for ipsilateral and contralateral hand movements

The caudal cingulate motor area (CMAc) and the supplementary motor area (SMA) play important roles in movement execution. The present study aimed to characterize the functional organization of these regions during movement by investigating laterality representations in the CMAc and SMA of monkeys via an examination of neuronal activity during a button press movement with either the right or left hand. Three types of movement-related neuronal activity were observed: 1) with only the contralateral hand, 2) with only the ipsilateral hand, and 3) with either hand. Neurons in the CMAc represented contralateral and ipsilateral hand movements to the same degree, whereas neuronal representations in the SMA were biased toward contralateral hand movement. Furthermore, recording neuronal activities using a linear-array multicontact electrode with 24 contacts spaced 150 μm apart allowed us to analyze the spatial distribution of neurons exhibiting particular hand preferences at the submillimeter scale. The CMAc and SMA displayed distinct microarchitectural organizations. The contralateral, ipsilateral, and bilateral CMAc neurons were distributed homogeneously, whereas SMA neurons exhibiting identical hand preferences tended to cluster. These findings indicate that the CMAc, which is functionally organized in a less structured manner than the SMA is, controls contralateral and ipsilateral hand movements in a counterbalanced fashion, whereas the SMA, which is more structured, preferentially controls contralateral hand movements.

fMRI Cortical Correlates of Spontaneous Eye Blinks in the Nonhuman Primate

Eyeblinks are defined as a rapid closing and opening of the eyelid. Three types of blinks are defined: spontaneous, reflexive, and voluntary. Here, we focus on the cortical correlates of spontaneous blinks, using functional magnetic resonance imaging (fMRI) in the nonhuman primate. Our observations reveal an ensemble of cortical regions processing the somatosensory, proprioceptive, peripheral visual, and possibly nociceptive consequences of blinks. These observations indicate that spontaneous blinks have consequences on the brain beyond the visual cortex, possibly contaminating fMRI protocols that generate in the participants heterogeneous blink behaviors. This is especially the case when these protocols induce (nonunusual) eye fatigue and corneal dryness due to demanding fixation requirements, as is the case here. Importantly, no blink related activations were observed in the prefrontal and parietal blinks motor command areas nor in the prefrontal, parietal, and medial temporal blink suppression areas. This indicates that the absence of activation in these areas is not a signature of the absence of blink contamination in the data. While these observations increase our understanding of the neural bases of spontaneous blinks, they also strongly call for new criteria to identify whether fMRI recordings are contaminated by a heterogeneous blink behavior or not.

Effects of unilateral deactivations of dorsolateral prefrontal cortex and anterior cingulate cortex on saccadic eye movements

The dorsolateral prefrontal cortex (dlPFC) and anterior cingulate cortex (ACC) have both been implicated in the cognitive control of saccadic eye movements by single neuron recording studies in nonhuman primates and functional imaging studies in humans, but their relative roles remain unclear. Here, we reversibly deactivated either dlPFC or ACC subregions in macaque monkeys while the animals performed randomly interleaved pro- and antisaccades. In addition, we explored the whole-brain functional connectivity of these two regions by applying a seed-based resting-state functional MRI analysis in a separate cohort of monkeys. We found that unilateral dlPFC deactivation had stronger behavioral effects on saccades than unilateral ACC deactivation, and that the dlPFC displayed stronger functional connectivity with frontoparietal areas than the ACC. We suggest that the dlPFC plays a more prominent role in the preparation of pro- and antisaccades than the ACC.

Anomalous use of context during task preparation in schizophrenia: a magnetoencephalography study

BACKGROUND

Impaired ability to use contextual information to optimally prepare for tasks contributes to performance deficits in schizophrenia. We used magnetoencephalography and an antisaccade task to investigate the neural basis of this deficit.

METHODS

In schizophrenia patients and healthy control participants, we examined the difference in preparatory activation to cues indicating an impending antisaccade or prosaccade. We analyzed activation for correct trials only and focused on the network for volitional ocular motor control-frontal eye field (FEF), dorsal anterior cingulate cortex (dACC), and the ventrolateral and dorsolateral prefrontal cortex (VLPFC, DLPFC).

RESULTS

Compared with control subjects, patients made more antisaccade errors and showed reduced differential preparatory activation in the dACC and increased differential preparatory activation in the VLPFC. In patients only, antisaccade error rates correlated with preparatory activation in the FEF, DLPFC, and VLPFC.

CONCLUSIONS

In schizophrenia, reduced differential preparatory activation of the dACC may reflect reduced signaling of the need for control. Greater preparatory activation in the VLPFC and the correlations of error rate with FEF, DLPFC, and VLPFC activation may reflect that patients who are more error prone require stronger activation in these regions for correct performance. These findings provide the first evidence of abnormal task preparation, distinct from response generation, during volitional saccades in schizophrenia. We conclude that schizophrenia patients are impaired in using task cues to modulate cognitive control and that this contributes to deficits inhibiting prepotent but contextually inappropriate responses and to behavior that is stimulus bound and error prone rather than flexibly guided by context.

Neuroimaging evidence of the anatomo-functional organization of the human cingulate motor areas

In the monkey, 3 motor areas have been identified in the cortex occupying the banks of the cingulate sulcus (cgs): A rostral cingulate motor area and 2 caudal cingulate motor areas, 1 located in the dorsal bank and the other in the ventral bank of the sulcus. The homologs of these 3 cingulate motor areas in the human brain are poorly understood. The present functional magnetic resonance imaging study examined the anatomo-functional organization of the cingulate motor areas in the human brain. A subject by subject analysis revealed the existence of 3 motor areas along the cgs and these areas appear to be somatotopically organized. Importantly, these 3 motor areas relate to the specific morphological features of the cingulate/paracingulate cortex. These results demonstrate the location and organization of the 3 cingulate motor areas in the human brain and suggest a well-preserved organization of these motor areas from the monkey to the human brain.

Functional connectivity of the frontal eye fields in humans and macaque monkeys investigated with resting-state fMRI

Although the frontal eye field (FEF) has been identified in macaque monkeys and humans, practical constraints related to invasiveness and task demands have limited a direct cross-species comparison of its functional connectivity. In this study, we used resting-state functional MRI data collected from both awake humans and anesthetized macaque monkeys to examine and compare the functional connectivity of the FEF. A seed region analysis revealed consistent ipsilateral functional connections of the FEF with fronto-parietal cortical areas across both species. These included the intraparietal sulcus, dorsolateral prefrontal cortex, anterior cingulate cortex, and supplementary eye fields. The analysis also revealed greater lateralization of connectivity with the FEF in both hemispheres in humans than in monkeys. Cortical surface-based transformation of connectivity maps between species further corroborated the remarkably similar organization of the FEF functional connectivity. The results support an evolutionarily preserved fronto-parietal system and provide a bridge for linking data from monkey and human studies.

Cytoarchitecture and cortical connections of the anterior cingulate and adjacent somatomotor fields in the rhesus monkey

The cytoarchitecture and cortical connections of the anterior cingulate, medial and dorsal premotor, and precentral region are investigated using the Nissl and NeuN staining methods and the fluorescent retrograde tract tracing technique. There is a gradual stepwise laminar change in the cytoarchitectonic organization from the proisocortical anterior cingulate region, through the lower and upper banks of the cingulate sulcus, to the dorsolateral isocortical premotor and precentral motor regions of the frontal lobe. These changes are characterized by a gradational emphasis on the lower stratum layers (V and VI) in the proisocortical cingulate region to the upper stratum layers (II and III) in the premotor and precentral motor region. This is accompanied by a progressive widening of layers III and VI, a poorly delineated border between layers III and V and a sequential increase in the size of layer V neurons culminating in the presence of giant Betz cells in the precentral motor region. The overall patterns of corticocortical connections paralleled the sequential changes in cytoarchitectonic organization. The proisocortical areas have connections with cingulate motor, supplementary motor, premotor and precentral motor areas on the one hand and have widespread connections with the frontal, parietal, temporal and multimodal association cortex and limbic regions on the other. The dorsal premotor areas have connections with the proisocortical areas including cingulate motor areas and supplementary motor area on the one hand, and premotor and precentral motor cortex on the other. Additionally, this region has significant connections with posterior parietal cortex and limited connections with prefrontal, limbic and multimodal regions. The precentral motor cortex also has connections with the proisocortical areas and premotor areas. Its other connections are limited to the somatosensory regions of the parietal lobe. Since the isocortical motor areas on the dorsal convexity mediate voluntary motor function, their close connectional relationship with the cingulate areas form a pivotal limbic-motor interface that could provide critical sources of cognitive, emotional and motivational influence on complex motor function.

Frontal cortex and reward-guided learning and decision-making

Reward-guided decision-making and learning depends on distributed neural circuits with many components. Here we focus on recent evidence that suggests four frontal lobe regions make distinct contributions to reward-guided learning and decision-making: the lateral orbitofrontal cortex, the ventromedial prefrontal cortex and adjacent medial orbitofrontal cortex, anterior cingulate cortex, and the anterior lateral prefrontal cortex. We attempt to identify common themes in experiments with human participants and with animal models, which suggest roles that the areas play in learning about reward associations, selecting reward goals, choosing actions to obtain reward, and monitoring the potential value of switching to alternative courses of action.

Resting-state connectivity identifies distinct functional networks in macaque cingulate cortex

Subregions of the cingulate cortex represent prominent intersections in the structural networks of the primate brain. The relevance of the cingulate to the structure and dynamics of large-scale networks ultimately requires a link to functional connectivity. Here, we map fine-grained functional connectivity across the complete extent of the macaque (Macaca fascicularis) cingulate cortex and delineate subdivisions pertaining to distinct identifiable networks. In particular, we identified 4 primary networks representing the functional spectrum of the cingulate: somatomotor, attention-orienting, executive, and limbic. The cingulate nodes of these networks originated from separable subfields along the rostral-to-caudal axis and were characterized by positive and negative correlations of spontaneous blood oxygen level-dependent activity. These findings represent a critical component for understanding how the anterior and midcingulate cortices integrate and shape information processing during task performance. The connectivity patterns also suggest future electrophysiological targets that may reveal new functional representations including those involved in conflict monitoring.

Inter-individual decision-making differences in the effects of cingulate, orbitofrontal, and prelimbic cortex lesions in a rat gambling task

Deficits in decision-making is a hallmark of several neuropsychiatric pathologies but is also observed in some healthy individuals that could be at risk to develop these pathologies. Poor decision-making can be revealed experimentally in humans using the Iowa gambling task, through the inability to select options that ensure long term gains over larger immediate gratification. We devised an analogous task in the rat, based on uncertainty and conflicting choices, the rat gambling task (RGT). It similarly reveals good and poor performers within a single session. Using this task, we investigated the role of three prefrontal cortical areas, the orbitofrontal, prelimbic, and cingulate cortices on decision-making, taking into account inter-individual variability in behavioral performances. Here, we show that these three distinct subregions are differentially engaged to solve the RGT. Cingulate cortex lesion mainly delayed good decision-making whereas prelimbic and orbitofrontal cortices induced different patterns of inadapted behaviors in the task, indicating varying degree of functional specialization of these three areas. Their contribution largely depended on the level of adaptability demonstrated by each individual to the constraint of the task. The inter-individual differences in the effect of prefrontal cortex area lesions on decision-making revealed in this study open new perspectives in the search for vulnerability markers to develop disorders related to executive dysfunctioning.

Medio-frontal and anterior temporal abnormalities in children with attention deficit hyperactivity disorder (ADHD) during an acoustic antisaccade task as revealed by electro-cortical source reconstruction

BACKGROUND

Attention Deficit Hyperactivity Disorder (ADHD) is one of the most prevalent disorders in children and adolescence. Impulsivity is one of three core symptoms and likely associated with inhibition difficulties. To date the neural correlate of the antisaccade task, a test of response inhibition, has not been studied in children with (or without) ADHD.

METHODS

Antisaccade responses to visual and acoustic cues were examined in nine unmedicated boys with ADHD (mean age 122.44 ± 20.81 months) and 14 healthy control children (mean age 115.64 ± 22.87 months, three girls) while an electroencephalogram (EEG) was recorded. Brain activity before saccade onset was reconstructed using a 23-source-montage.

RESULTS

When cues were acoustic, children with ADHD had a higher source activity than control children in Medio-Frontal Cortex (MFC) between -230 and -120 ms and in the left-hemispheric Temporal Anterior Cortex (TAC) between -112 and 0 ms before saccade onset, despite both groups performing similarly behaviourally (antisaccades errors and saccade latency). When visual cues were used EEG-activity preceding antisaccades did not differ between groups.

CONCLUSION

Children with ADHD exhibit altered functioning of the TAC and MFC during an antisaccade task elicited by acoustic cues. Children with ADHD need more source activation to reach the same behavioural level as control children.

Reduced cognitive control of response inhibition by the anterior cingulate cortex in autism spectrum disorders

Response inhibition, or the suppression of prepotent, but contextually inappropriate behaviors, is essential to adaptive, flexible responding. In autism spectrum disorders (ASD), difficulty inhibiting prepotent behaviors may contribute to restricted, repetitive behavior (RRB). Individuals with ASD consistently show deficient response inhibition while performing antisaccades, which require one to inhibit the prepotent response of looking towards a suddenly appearing stimulus (i.e., a prosaccade), and to substitute a gaze in the opposite direction. Here, we used fMRI to identify the neural correlates of this deficit. We focused on two regions that are critical for saccadic inhibition: the frontal eye field (FEF), the key cortical region for generating volitional saccades, and the dorsal anterior cingulate cortex (dACC), which is thought to exert top-down control on the FEF. We also compared ASD and control groups on the functional connectivity of the dACC and FEF during saccadic performance. In the context of an increased antisaccade error rate, ASD participants showed decreased functional connectivity of the FEF and dACC and decreased inhibition-related activation (based on the contrast of antisaccades and prosaccades) in both regions. Decreased dACC activation correlated with a higher error rate in both groups, consistent with a role in top-down control. Within the ASD group, increased FEF activation and dACC/FEF functional connectivity were associated with more severe RRB. These findings demonstrate functional abnormalities in a circuit critical for volitional ocular motor control in ASD that may contribute to deficient response inhibition and to RRB. More generally, our findings suggest reduced cognitive control over behavior by the dACC in ASD.

Performance monitoring local field potentials in the medial frontal cortex of primates: supplementary eye field

We describe intracranial local field potentials (LFPs) recorded in the supplementary eye field (SEF) of macaque monkeys performing a saccade countermanding task. The most prominent feature at 90% of the sites was a negative-going polarization evoked by a contralateral visual target. At roughly 50% of sites a negative-going polarization was observed preceding saccades, but in stop signal trials this polarization was not modulated in a manner sufficient to control saccade initiation. When saccades were canceled in stop signal trials, LFP modulation increased with the inferred magnitude of response conflict derived from the coactivation of gaze-shifting and gaze-holding neurons. At 30% of sites, a pronounced negative-going polarization occurred after errors. This negative polarity did not appear in unrewarded correct trials. Variations of response time with trial history were not related to any features of the LFP. The results provide new evidence that error-related and conflict-related but not feedback-related signals are conveyed by the LFP in the macaque SEF and are important for identifying the generator of the error-related negativity.

Saccadic preparation in the frontal eye field is modulated by distinct trial history effects as revealed by magnetoencephalography

Optimizing outcomes involves rapidly and continuously adjusting behavior based on context. While most behavioral studies focus on immediate task conditions, responses to events are also influenced by recent history. We used magnetoencephalography and a saccadic paradigm to investigate the neural bases of 2 trial history effects that are well characterized in the behavioral eye movement literature: task-switching and the prior-antisaccade effect. We found that switched trials were associated with increased errors and transient increases in activity in the frontal eye field (FEF) and anterior cingulate cortex early in the preparatory period. These activity changes are consistent with active reconfiguration of the task set, a time-limited process that is triggered by the instructional cue. Following an antisaccade versus prosaccade, there was increased activity in the FEF and prefrontal cortex that persisted into the preparatory period of the subsequent trial, and saccadic latencies were prolonged. We attribute these effects to persistent inhibition of the ocular motor response system from the prior antisaccade. These findings refine our understanding of how trial history interacts with current task demands to adjust responses. Such dynamic modulations of neural activity and behavior by recent experience are at the heart of adaptive flexible behavior.

Effects of anterior cingulate microstimulation on pro- and antisaccades in nonhuman primates

Numerous studies have established a role for the ACC in cognitive control. Current theories are at odds as to whether ACC itself directly engages or alternatively recruits other frontal cortical areas that implement control. The antisaccade task, in which subjects are required to make a saccade to the location opposite a suddenly appearing visual stimulus, is a simple oculomotor paradigm that has been used extensively to investigate flexible oculomotor control. Here, we tested a causal role of the dorsal ACC in cognitive control by applying electrical microstimulation during a preparatory period while monkeys performed alternating blocks of pro- and antisaccade trials. Microstimulation induced significant changes in saccadic RTs (SRTs) in both tasks. On prosaccade trials, SRTs were increased for saccades contralateral to and decreased for saccades ipsilateral to the stimulated hemisphere. In contrast, SRTs were decreased for both ipsi- and contralaterally directed antisaccades. These data show that microstimulation administered during response preparation facilitated the performance of antisaccades and are suggestive of a direct role of ACC in the implementation of cognitive control.

Supplementary eye field activity reflects a decision rule governing smooth pursuit but not the decision

Animals depend on learned rules to guide their actions. Prefrontal (PFC) and premotor (PMC) cortex of primates have been reported to display rule-related neural activity, but it is unclear how signals encoded here are utilized to enforce the decision to act. The supplementary eye field (SEF) is a candidate for enforcing rule-guided ocular decisions because the activity of neurons here is correlated with the rule in an ocular decision-making task and because this area is anatomically more proximal to movement structures than PFC and PMC and receives inputs from them. However, in the previous work, the rule encoding and ocular outcome were confounded, leaving open the question of whether SEF activity is related to the rule or the behavior. In the present study, we attempted to discriminate between these alternatives by increasing task difficulty and forcing errors, thereby putting the stimulus and the behavior at odds. Single SEF neurons were recorded while monkeys performed the task in which the rule is to pursue a moving target if it intersects a visible square and maintain fixation if it does not. A delay period was imposed to monitor neural activity while the target approached the square. Two complementary populations of go and nogo neurons were found. When task difficulty was increased, the monkeys made more errors, and the neurons took longer to encode the rule. However, in error trials, most neurons continued to reflect the rule rather the monkey's ocular decision in both the delay period and after square intersection (movement period). This was the case for both directionally tuned and nondirectional SEF neurons. The results suggest that SEF neurons encode the ocular decision rule but that the decision itself likely occurs in a different structure that sums rule information from the SEF with information from other areas.

Connectivity-based parcellation of human cingulate cortex and its relation to functional specialization

Whole-brain neuroimaging studies have demonstrated regional variations in function within human cingulate cortex. At the same time, regional variations in cingulate anatomical connections have been found in animal models. It has, however, been difficult to estimate the relationship between connectivity and function throughout the whole cingulate cortex within the human brain. In this study, magnetic resonance diffusion tractography was used to investigate cingulate probabilistic connectivity in the human brain with two approaches. First, an algorithm was used to search for regional variations in the probabilistic connectivity profiles of all cingulate cortex voxels with the whole of the rest of the brain. Nine subregions with distinctive connectivity profiles were identified. It was possible to characterize several distinct areas in the dorsal cingulate sulcal region. Several distinct regions were also found in subgenual and perigenual cortex. Second, the probabilities of connection between cingulate cortex and 11 predefined target regions of interest were calculated. Cingulate voxels with a high probability of connection with the different targets formed separate clusters within cingulate cortex. Distinct connectivity fingerprints characterized the likelihood of connections between the extracingulate target regions and the nine cingulate subregions. Last, a meta-analysis of 171 functional studies reporting cingulate activation was performed. Seven different cognitive conditions were selected and peak activation coordinates were plotted to create maps of functional localization within the cingulate cortex. Regional functional specialization was found to be related to regional differences in probabilistic anatomical connectivity.

Frontal cortex subregions play distinct roles in choices between actions and stimuli

The orbitofrontal cortex (OFC) has been implicated in reinforcement-guided decision making, error monitoring, and the reversal of behavior in response to changing circumstances. The anterior cingulate cortex sulcus (ACC(S)), however, has also been implicated in similar aspects of behavior. Dissociating the unique functions of these areas would improve our understanding of the decision-making process. The effect of selective OFC lesions on how monkeys used the history of reinforcement to guide choices of either particular actions or particular stimuli was studied and compared with the effects of ACC(S) lesions. Both lesions disrupted decision making, but their effects were differentially modulated by the dependence on action- or stimulus-value contingencies. OFC lesions caused a deficit in stimulus but not action selection, whereas ACC(S) lesions had the opposite effect, disrupting action but not stimulus selection. Furthermore, OFC lesions that have previously been found to impair decision making when deterministic stimulus-reward contingencies are switched were found to cause a more general learning impairment in more naturalistic situations in which reward was stochastic. Both OFC and ACC(S) are essential for reinforcement-guided decision making rather than just error monitoring or behavioral reversal. The OFC and ACC(S) are both, however, more concerned with learning and making decisions, but their roles in selecting between stimulus and action values are distinct.

BOLD fMRI activation for anti-saccades in nonhuman primates

Most of our knowledge about the functional organization of the nonhuman primate brain has come from single neuron recordings, whereas functional magnetic resonance imaging (fMRI) has rapidly become the method of choice for the study of the human brain. In some cases these two methods have resulted in conflicting models of frontal lobe function. Based on the finding that the frontal eye fields (FEF) exhibit a higher blood-oxygenation-level dependent (BOLD) activation for anti-saccades compared with pro-saccades, it has been proposed that this area is more involved in voluntary than automatic saccade generation. This model has been questioned by the finding of decreased single neuron activity in FEF for anti-compared with pro-saccades in monkeys. To reconcile these findings, we employed fMRI to compare BOLD activation between anti-saccades and pro-saccades in monkeys. FEF and a number of other cortical and subcortical areas showed an increased activation for anti-saccades. The results indicate that previous contrary findings between single neuron recordings and fMRI were due to differences between these techniques and were not related to differences between the two primate species.

Connectivity of the primate superior colliculus mapped by concurrent microstimulation and event-related FMRI

Background

Neuroanatomical studies investigating the connectivity of brain areas have heretofore employed procedures in which chemical or viral tracers are injected into an area of interest, and connected areas are subsequently identified using histological techniques. Such experiments require the sacrifice of the animals and do not allow for subsequent electrophysiological studies in the same subjects, rendering a direct investigation of the functional properties of anatomically identified areas impossible.

Methodology/Principal Findings

Here, we used a combination of microstimulation and fMRI in an anesthetized monkey preparation to study the connectivity of the superior colliculus (SC). Microstimulation of the SC resulted in changes in the blood oxygenation level-dependent (BOLD) signals in the SC and in several cortical and subcortical areas consistent with the known connectivity of the SC in primates.

Conclusions/Significance

These findings demonstrates that the concurrent use of microstimulation and fMRI can be used to identify brain networks for further electrophysiological or fMRI investigation.

Performance monitoring local field potentials in the medial frontal cortex of primates: anterior cingulate cortex

We describe intracranial local field potentials (LFP) recorded in the anterior cingulate cortex (ACC) of macaque monkeys performing a saccade countermanding task. The most prominent feature at approximately 70% of sites was greater negative polarity after errors than after rewarded correct trials. This negative polarity was also evoked in unrewarded correct trials. The LFP evoked by the visual target was much less polarized, and the weak presaccadic modulation was insufficient to control the initiation of saccades. When saccades were cancelled, LFP modulation decreased slightly with the magnitude of response conflict that corresponds to the coactivation of gaze-shifting and -holding neurons estimated from the probability of canceling. However, response time adjustments on subsequent trials were not correlated with LFP polarity on individual trials. The results provide clear evidence that error- and feedback-related, but not conflict-related, signals are carried by the LFP in the macaque ACC. Finding performance monitoring field potentials in the ACC of macaque monkeys establishes a bridge between event-related potential and functional brain-imaging studies in humans and neurophysiology studies in non-human primates.

Spatial distribution of cingulate cortical cells projecting to the primary motor cortex in the rat

We examined the location and spatial distribution of cingulate cortical cells projecting to the primary motor cortex (M1) in rats, using a double retrograde-labeling technique. The orofacial, forelimb, and hindlimb areas of M1 were physiologically identified based on the findings of intracortical microstimulation and single cell recording. Two different tracers, diamidino yellow and fast blue, were injected into two sites of M1 in each rat. Retrograde-labeled cells in the cingulate cortex were plotted with an automated plotting system. Cells projecting to the orofacial and forelimb areas of M1 were distributed in the anterior cingulate cortex (area 24) but not in the posterior cingulate cortex (retrosplenial cortex; area 29), according to topographical mapping. On the other hand, few or no cells of the cingulate cortex were observed projecting to the hindlimb area of M1. These findings suggest that the cingulate cortex projecting to the M1 in the rat are involved in the regulation of motor activity that involves the orofacial and forelimb, but not hindlimb, parts of the body.

Frontoparietal Activation With Preparation for Antisaccades

Several current models hold that frontoparietal areas exert cognitive control by biasing task-relevant processing in other brain areas. Previous event-related functional magnetic resonance imaging (fMRI) studies have compared prosaccades and antisaccades, which require subjects to look toward or away from a flashed peripheral stimulus, respectively. These studies found greater activation for antisaccades in frontal and parietal regions at the ends of long (≥6 s) preparatory periods preceding peripheral stimulus presentation. Event-related fMRI studies using short preparatory periods (≤4 s) have not found such activation differences except in the frontal eye field. Here, we identified activation differences associated with short (1-s) preparatory periods by interleaving half trials among regular whole trials in a rapid fMRI design. On whole trials, a colored fixation dot instructed human subjects to make either a prosaccade toward or an antisaccade away from a peripheral visual stimulus. Half trials included only the instruction and not peripheral stimulus presentation or saccade generation. Nonetheless, half trials evoked stronger activation on antisaccades than on prosaccades in the frontal eye field (FEF), supplementary eye field (SEF), left dorsolateral prefrontal cortex (DLPFC), anterior cingulate cortex (ACC), intraparietal sulcus (IPS), and precuneus. Greater antisaccade response-related activation was found in FEF, SEF, IPS, and precuneus but not in DLPFC or ACC. These results demonstrate greater preparatory activation for antisaccades versus prosaccades in frontoparietal areas and suggest that prefrontal cortex and anterior cingulate cortex are more involved in presetting the saccade network for the antisaccade task than generating the actual antisaccade response.

Top-down control-signal dynamics in anterior cingulate and prefrontal cortex neurons following task switching

The prefrontal cortex (PFC) and anterior cingulate cortex (ACC) have both been implicated in cognitive control, but their relative roles remain unclear. Here we recorded the activity of single neurons in both areas while monkeys performed a task that required them to switch between trials in which they had to look toward a flashed stimulus (prosaccades) and trials in which they had to look away from the stimulus (antisaccades). We found that ACC neurons had a higher level of task selectivity than PFC neurons during the preparatory period on trials immediately following a task switch. In ACC neurons, task selectivity was strongest after the task switch and declined throughout the task block, whereas task selectivity remained constant in the PFC. These results demonstrate that the ACC is recruited when cognitive demands increase and suggest a role for both areas in task maintenance and the implementation of top-down control.

Contrasting roles for cingulate and orbitofrontal cortex in decisions and social behaviour

There is general acknowledgement that both the anterior cingulate and orbitofrontal cortex are implicated in reinforcement-guided decision making, and emotion and social behaviour. Despite the interest that these areas generate in both the cognitive neuroscience laboratory and the psychiatric clinic, ideas about the distinctive contributions made by each have only recently begun to emerge. This reflects an increasing understanding of the component processes that underlie reinforcement-guided decision making, such as the representation of reinforcement expectations, the exploration, updating and representation of action values, and the appreciation that choices are guided not just by the prospect of reward but also by the costs that action entails. Evidence is emerging to suggest that the anterior cingulate and orbitofrontal cortex make distinct contributions to each of these aspects of decision making.

Amygdala interconnections with the cingulate motor cortex in the rhesus monkey

Amygdala interconnections with the cingulate motor cortices were investigated in the rhesus monkey. Using multiple tracing approaches, we found a robust projection from the lateral basal nucleus of the amygdala to Layers II, IIIa, and V of the rostral cingulate motor cortex (M3). A smaller source of amygdala input arose from the accessory basal, cortical, and lateral nuclei, which targeted only the rostral region of M3. We also found a light projection from the lateral basal nucleus to the same layers of the caudal cingulate motor cortex (M4). Experiments examining this projection to cingulate somatotopy using combined neural tracing strategies and stereology to estimate the total number of terminal-like immunoreactive particles demonstrated that the amygdala projection terminates heavily in the face representation of M3 and moderately in its arm representation. Fewer terminal profiles were found in the leg representation of M3 and the face, arm, and leg representations of M4. Anterograde tracers placed directly into M3 and M4 revealed the amygdala connection to be reciprocal and documented corticofugal projections to the facial nucleus, surrounding pontine reticular formation, and spinal cord. Clinically, such pathways would be in a position to contribute to mediating movements in the face, neck, and upper extremity accompanying medial temporal lobe seizures that have historically characterized this syndrome. Alterations within or disruption of the amygdalo-cingulate projection to the rostral part of M3 may also have an adverse effect on facial expression in patients presenting with neurological or neuropsychiatric abnormalities of medial temporal lobe involvement. Finally, the prominent amygdala projection to the face region of M3 may significantly influence the outcome of higher-order facial expressions associated with social communication and emotional constructs such as fear, anger, happiness, and sadness.

Prefrontal cortical cells projecting to the supplementary eye field and presupplementary motor area in the monkey

We examined the location and spatial distribution of prefrontal cortical (PF) cells projecting to the supplementary eye field (SEF) and presupplementary motor area (pre-SMA) using a double retrograde-labeling technique in monkeys (Macaca fuscata). The SEF and pre-SMA were physiologically identified based on the findings of intracortical microstimulation and single cell recordings. Two fluorescent tracers, diamidino yellow and fast blue, were injected into the SEF and pre-SMA of each monkey. Retrogradely labeled cells in the PF were plotted with an automated plotting system. The cells projecting to the SEF and pre-SMA were mainly distributed in the upper and lower banks of the principal sulcus (area 46), with little overlap. Cells projecting to the SEF, but not to the pre-SMA, were observed in areas 8a, 8b, 9, 12, and 45. These findings suggest that the SEF and pre-SMA receive different sets of information from the PF cells.

Chronometry of visual responses in frontal eye field, supplementary eye field, and anterior cingulate cortex

The latency and variability of latency of single-unit responses to identical visual stimulation were measured in the frontal eye field (FEF), supplementary eye field (SEF), and anterior cingulate cortex (ACC) of macaque monkeys performing visually guided saccades. The mean visual response latency was significantly shorter in FEF (64 ms) than in SEF (81 ms) or ACC (100 ms), and latency values determined by four methods agreed. The latency variability of the visual response was respectively less in FEF (21 ms) than in SEF (37 ms) or ACC (41 ms). Latency, variability of latency, and magnitude of the visual responses were correlated within FEF and SEF but not ACC. These characteristics of the visual response are consistent with the degree of convergence of visual afferents to these areas and constrain hypotheses about visual processing in the frontal lobe.

The primate working memory networks

Working memory has long been associated with the prefrontal cortex, since damage to this brain area can critically impair the ability to maintain and update mnemonic information. Anatomical and physiological evidence suggests, however, that the prefrontal cortex is part of a broader network of interconnected brain areas involved in working memory. These include the parietal and temporal association areas of the cerebral cortex, cingulate and limbic areas, and subcortical structures such as the mediodorsal thalamus and the basal ganglia. Neurophysiological studies in primates confirm the involvement of areas beyond the frontal lobe and illustrate that working memory involves parallel, distributed neuronal networks. In this article, we review the current understanding of the anatomical organization of networks mediating working memory and the neural correlates of memory manifested in each of their nodes. The neural mechanisms of memory maintenance and the integrative role of the prefrontal cortex are also discussed.