The anterior thalamus provides a subcortical circuit supporting memory and spatial navigation

Mammillothalamic Disconnection Alters Hippocampocortical Oscillatory Activity and Microstructure: Implications for Diencephalic Amnesia

Diencephalic amnesia can be as debilitating as the more commonly known temporal lobe amnesia, yet the precise contribution of diencephalic structures to memory processes remains elusive. Across four cohorts of male rats, we used discrete lesions of the mammillothalamic tract to model aspects of diencephalic amnesia and assessed the impact of these lesions on multiple measures of activity and plasticity within the hippocampus and retrosplenial cortex. Lesions of the mammillothalamic tract had widespread indirect effects on hippocampocortical oscillatory activity within both theta and gamma bands. Both within-region oscillatory activity and cross-regional synchrony were altered. The network changes were state-dependent, displaying different profiles during locomotion and paradoxical sleep. Consistent with the associations between oscillatory activity and plasticity, complementary analyses using several convergent approaches revealed microstructural changes, which appeared to reflect a suppression of learning-induced plasticity in lesioned animals. Together, these combined findings suggest a mechanism by which damage to the medial diencephalon can impact upon learning and memory processes, highlighting an important role for the mammillary bodies in the coordination of hippocampocortical activity.SIGNIFICANCE STATEMENT Information flow within the Papez circuit is critical to memory. Damage to ascending mammillothalamic projections has consistently been linked to amnesia in humans and spatial memory deficits in animal models. Here we report on the changes in hippocampocortical oscillatory dynamics that result from chronic lesions of the mammillothalamic tract and demonstrate, for the first time, that the mammillary bodies, independently of the supramammillary region, contribute to frequency modulation of hippocampocortical theta oscillations. Consistent with the associations between oscillatory activity and plasticity, the lesions also result in a suppression of learning-induced plasticity. Together, these data support new functional models whereby mammillary bodies are important for coordinating hippocampocortical activity rather than simply being a relay of hippocampal information as previously assumed.

Cerebral perfusion mapping during retrieval of spatial memory in rats

Studies of brain functional activation during spatial navigation using electrophysiology and immediate-early gene responses have typically targeted a limited number of brain regions. Our study provides the first whole brain analysis of cerebral activation during retrieval of spatial memory in the freely-moving rat. Rats (LEARNERS) were trained in the Barnes maze, an allocentric spatial navigation task, while CONTROLS received passive exposure. After 19 days, functional brain mapping was performed during recall by bolus intravenous injection of [¹⁴C]-iodoantipyrine using a novel subcutaneous minipump triggered by remote activation. Regional cerebral blood flow (rCBF)-related tissue radioactivity was analyzed by statistical parametric mapping from autoradiographic images of the three-dimensionally reconstructed brains. Functional connectivity was examined between regions of the spatial navigation circuit through interregional correlation analysis. Significant rCBF increases were noted in LEARNERS compared to CONTROLS broadly across the spatial navigation circuit, including the hippocampus (anterior dorsal CA1, posterior ventral CA1-3), subiculum, thalamus, striatum, medial septum, cerebral cortex, with decreases noted in the mammillary nucleus, amygdala and insula. LEARNERS showed a significantly greater positive correlation of rCBF of the ventral hippocampus with retrosplenial, lateral orbital, parietal and primary visual cortex, and a significantly more negative correlation with the mammillary nucleus, amygdala, posterior entorhinal cortex, and anterior thalamic nucleus. The complex sensory component of the spatial navigation task was underscored by broad activation across visual, somatosensory, olfactory, auditory and vestibular circuits which was enhanced in LEARNERS. Brain mapping facilitated by an implantable minipump represents a powerful tool for evaluation of mammalian behaviors dependent on locomotion.

Fractional Anisotropy of Thalamic Nuclei Is Associated With Verticality Misperception After Extra-Thalamic Stroke

Verticality misperception after stroke is a frequent neurological deficit that leads to postural imbalance and a higher risk of falls. The posterior thalamic nuclei are described to be involved with verticality perception, but it is unknown if extra-thalamic lesions can have the same effect via diaschisis and degeneration of thalamic nuclei. We investigated the relationship between thalamic fractional anisotropy (FA, a proxy of structural integrity), and verticality perception, in patients after stroke with diverse encephalic extra-thalamic lesions. We included 11 first time post-stroke patients with extra-thalamic primary lesions, and compared their region-based FA to a group of 25 age-matched healthy controls. For the patient sample, correlation and regression analyses evaluated the relationship between thalamic nuclei FA and error of postural vertical (PV) and haptic vertical (HV) in the roll (PVroll/HVroll) and pitch planes (PVpitch/HVpitch). Relative to controls, patients showed decreased FA of anterior, ventral anterior, ventral posterior lateral, dorsal, and pulvinar thalamic nuclei, despite the primary lesions being extra-thalamic. We found a significant correlation between HVroll, and FA in the anterior and dorsal nuclei, and PVroll with FA in the anterior nucleus. FA in the anterior, ventral anterior, ventral posterior lateral, dorsal and pulvinar nuclei predicted PV, and FA in the ventral anterior, ventral posterior lateral and dorsal nuclei predicted HV. While prior studies indicate that primary lesions of the thalamus can result in verticality misperception, here we present evidence supporting that secondary degeneration of thalamic nuclei via diaschisis can also be associated with verticality misperception after stroke.

Considering the Evidence for Anterior and Laterodorsal Thalamic Nuclei as Higher Order Relays to Cortex

Our memories are essential in our daily lives. The frontal and cingulate cortices, hippocampal system and medial temporal lobes are key brain regions. In addition, severe amnesia also occurs after damage or dysfunction to the anterior thalamic nuclei; this subcortical thalamic hub is interconnected to these key cortical memory structures. Behavioral, anatomical, and physiological evidence across mammalian species has shown that interactions between the anterior thalamic nuclei, cortex and hippocampal formation are vital for spatial memory processing. Furthermore, the adjacent laterodorsal thalamic nucleus (LD), interconnected to the retrosplenial cortex (RSC) and visual system, also contributes to spatial memory in mammals. However, how these thalamic nuclei contribute to memory still remains largely unknown. Fortunately, our understanding of the importance of the thalamus in cognitive processes is being redefined, as widespread evidence challenges the established view of the thalamus as a passive relay of sensory and subcortical information to the cortex. In this review article, we examine whether the anterior thalamic nuclei and the adjacent LD are suitable candidates for "higher-order" thalamic nuclei, as defined by the Sherman and Guillery model. Rather than simply relaying information to cortex, "higher-order" thalamic nuclei have a prominent role in cognition, as they can regulate how areas of the cortex interact with one another. These considerations along with a review of the latest research will be used to suggest future studies that will clarify the contributions that the anterior and LD have in supporting cortical functions during cognitive processes.

CREB down-regulation in the laterodorsal thalamic nucleus deteriorates memory consolidation in rats

The laterodorsal thalamic nucleus (LD) is believed to play roles in learning and memory, especially spatial tasks. However, the molecular mechanism that underlies the cognitive process in the LD remains unclear and needs to be investigated. So far, there is plenty of evidence indicating that plasticity has been in some of the cortical or subcortical regions closely related to the LD, particularly stimulated by external learning tasks. Therefore, the present study aimed to test the hypothesis that similar effect exists in the LD. The transcription factor, cAMP-response element binding protein (CREB), works essentially in brain plasticity by tightly regulating the transcriptional level of memory-related target genes, and the increase of activated CREB (phosphorylated CREB, p-CREB) could facilitate memory consolidation. In this study, the siRNA against CREB was synthesized to down-regulate the CREB mRNA in the LD. After Morris water maze behavioral training, CREB siRNA rats exhibited a memory deficiency, significantly diverging from the control groups. In subsequent detection, the expression of p-CREB of these memory impairment rats attenuated. These results support the hypothesis that CREB-mediated plasticity contributes to memory facilitation and consolidation in the LD.

Association between NRGN gene polymorphism and resting-state hippocampal functional connectivity in schizophrenia

BACKGROUND

Based on genome-wide association studies, a single-nucleotide polymorphism in the NRGN gene (rs12807809) is considered associated with schizophrenia (SZ). Moreover, hippocampal dysfunction is associated with rs12807809. In addition, converging evidence suggests that hippocampal dysfunction is involved in SZ pathophysiology. However, the association among rs12807809, hippocampal dysfunction and SZ pathophysiology is unknown. Therefore, this study investigated the association between rs12807809 and hippocampal functional connectivity at rest in SZ.

METHODS

In total, 158 participants were studied, including a C-carrier group carrying the non-risk C allele (29 SZ patients and 46 healthy controls) and a TT homozygous group carrying the risk T allele (30 SZ patients and 53 healthy controls). All participants were scanned using resting-state functional magnetic resonance imaging. Hippocampal functional connectivity was computed and compared among the 4 groups.

RESULTS

Significant main effects of diagnosis were observed in the functional connectivity between the hippocampus and bilateral fusiform gyrus, bilateral lingual gyrus, left inferior temporal gyrus, left caudate nucleus, bilateral thalamus and bilateral anterior cingulate gyri. In contrast, no significant main effect of genotype was found. In addition, a significant genotype by diagnosis interaction in the functional connectivity between the hippocampus and left anterior cingulate gyrus, as well as bilateral middle cingulate gyri, was observed, with TT homozygotes with SZ showing less functional connectivity than C-carriers with SZ and healthy control TT homozygotes.

CONCLUSIONS

These findings are the first to suggest an association between rs12807809 and abnormal Papez circuit function in patients with SZ. This study also implicates NRGN variation and abnormal Papez circuit function in SZ pathophysiology.

c-Fos expression in the limbic thalamus following thermoregulatory and wake-sleep changes in the rat

A cellular degeneration of two thalamic nuclei belonging to the "limbic thalamus", i.e., the anteroventral (AV) and mediodorsal (MD) nuclei, has been shown in patients suffering from Fatal Familial Insomnia (FFI), a lethal prion disease characterized by autonomic activation and severe insomnia. To better assess the physiological role of these nuclei in autonomic and sleep regulation, c-Fos expression was measured in rats during a prolonged exposure to low ambient temperature (T_a, - 10 °C) and in the first hours of the subsequent recovery period at normal laboratory T_a (25 °C). Under this protocol, the thermoregulatory and autonomic activation led to a tonic increase in waking and to a reciprocal depression in sleep occurrence, which was more evident for REM sleep. These effects were followed by a clear REM sleep rebound and by a rebound of Delta power during non-REM sleep in the following recovery period. In the anterior thalamic nuclei, c-Fos expression was (1) larger during the activity rather than the rest period in the baseline; (2) clamped at a level in-between the normal daily variation during cold exposure; (3) not significantly affected during the recovery period in comparison to the time-matched baseline. No significant changes were observed in either the MD or the paraventricular thalamic nucleus, which is also part of the limbic thalamus. The observed changes in the activity of the anterior thalamic nuclei appear, therefore, to be more specifically related to behavioral activation than to autonomic or sleep regulation.

A Resting-State Functional MR Imaging and Spectroscopy Study of the Dorsal Hippocampus in the Chronic Unpredictable Stress Rat Model

Exposure to chronic stress leads to an array of anatomical, functional, and metabolic changes in the brain that play a key role in triggering psychiatric disorders such as depression. The hippocampus is particularly well known as a target of maladaptive responses to stress. To capture stress-induced changes in metabolic and functional connectivity in the hippocampus, stress-resistant (low-responders) or -susceptible (high-responders) rats exposed to a chronic unpredictable stress paradigm (categorized according to their hormonal and behavioral responses) were assessed by multimodal neuroimaging; the latter was achieved by using localized ¹H MR spectroscopy and resting-state functional MRI (fMRI) at 11,7T data from stressed (n = 25) but also control (n = 15) male Wistar rats.Susceptible animals displayed increased GABA-glutamine (+19%) and glutamate-glutamine (+17%) ratios and decreased levels of macromolecules (-11%); these changes were positively correlated with plasma corticosterone levels. In addition, the neurotransmitter levels showed differential associations with functional connectivity between the hippocampus and the amygdala, the piriform cortex and thalamus between stress-resistant and -susceptible animals. Our observations are consistent with previously reported stress-induced metabolomic changes that suggest overall neurotransmitter dysfunction in the hippocampus. Their association with the fMRI data in this study reveals how local adjustments in neurochemistry relate to changes in the neurocircuitry of the hippocampus, with implications for its stress-associated dysfunctions.SIGNIFICANCE STATEMENT Chronic stress disrupts brain homeostasis, which may increase the vulnerability of susceptible individuals to neuropsychiatric disorders such as depression. Characterization of the differences between stress-resistant and -susceptible individuals on the basis of noninvasive imaging tools, such as magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI), contributes to improved understanding of the mechanisms underpinning individual differences in vulnerability and can facilitate the design of new diagnostic and intervention strategies. Using a combined functional MRI/MRS approach, our results demonstrate that susceptible- and non-susceptible subjects show differential alterations in hippocampal GABA and glutamate metabolism that, in turn, associate with changes in functional connectivity.

Papez's Forgotten Tract: 80 Years of Unreconciled Findings Concerning the Thalamocingulate Tract

The thalamocingulate tract is a key component of the Papez circuit that connects the anterior thalamic nucleus (ATN) to the cingulum bundle. While the other white matter connections, consisting of the fornix, cingulum bundle and mammillothalamic tract, were well defined in Papez's original 1937 paper, the anatomy of the thalamocingulate pathway was mentioned only in passing. Subsequent research has been unable to clarify the precise anatomical trajectory of this tract. In particular, the site of thalamocingulate tract interactions with the cingulum bundle have been inconsistently reported. This review aims to synthesize research on this least studied component of the Papez circuit. A systemic approach to reviewing historical anatomical dissection and neuronal tracing studies as well as contemporary diffusion magnetic resonance imaging studies of the thalamocingulate tract was undertaken across species. We found that although inconsistent, prior research broadly encompasses two differing descriptions of how the ATN interfaces with the cingulum after passing laterally through the anterior limb of the internal capsule. The first group of studies show that the pathway turns medially and rostrally and passes to the anterior cingulate region (Brodmann areas 24, 33, and 32) only. A second group suggests that the thalamocingulate tract interfaces with both the anterior and posterior cingulate (Brodmann areas 23 and 31) and retrosplenial region (Brodmann area 29). We discuss potential reasons for these discrepancies such as altering methodologies and species differences. We also discuss how these inconsistencies may be resolved in further research with refinements of terminology for the cingulate cortex and the thalamocingulate tract. Understanding the precise anatomical course of the last remaining unresolved final white matter tract in the Papez circuit may facilitate accurate investigation of the role of the complete Papez circuit in emotion and memory.

Dissociable Disruptions in Thalamic and Hippocampal Resting-State Functional Connectivity in Youth with 22q11.2 Deletions

The 22q11.2 deletion syndrome (22q11DS) is a recurrent copy number variant with high penetrance for developmental neuropsychiatric disorders. Study of individuals with 22q11DS therefore may offer key insights into neural mechanisms underlying such complex illnesses. Resting-state functional connectivity MRI studies in idiopathic schizophrenia have consistently revealed disruption of thalamic and hippocampal circuitry. Here, we sought to test whether this circuitry is similarly disrupted in the context of this genetic high-risk condition. To this end, resting-state functional connectivity patterns were assessed in a sample of human youth with 22q11DS (n = 42; 59.5% female) and demographically matched healthy controls (n = 39; 53.8% female). Neuroimaging data were acquired via single-band protocols and analyzed in line with methods provided by the Human Connectome Project. We computed functional relationships between individual-specific anatomically defined thalamic and hippocampal seeds and all gray matter voxels in the brain. Whole-brain Type I error protection was achieved through nonparametric permutation-based methods. The 22q11DS patients displayed dissociable disruptions in thalamic and hippocampal functional connectivity relative to control subjects. Thalamocortical coupling was increased in somatomotor regions and reduced across associative networks. The opposite effect was observed for the hippocampus in regards to somatomotor and associative network connectivity. The thalamic and hippocampal dysconnectivity observed in 22q11DS suggests that high genetic risk for psychiatric illness is linked with disruptions in large-scale corticosubcortical networks underlying higher-order cognitive functions. These effects highlight the translational importance of large-effect copy number variants for informing mechanisms underlying neural disruptions observed in idiopathic developmental neuropsychiatric disorders.SIGNIFICANCE STATEMENT Investigation of neuroimaging biomarkers in highly penetrant genetic syndromes represents a more biologically tractable approach to identify neural circuit disruptions underlying developmental neuropsychiatric conditions. The 22q11.2 deletion syndrome confers particularly high risk for psychotic disorders and is thus an important translational model in which to investigate systems-level mechanisms implicated in idiopathic illness. Here, we show resting-state fMRI evidence of large-scale sensory and executive network disruptions in youth with 22q11DS. In particular, this study provides the first evidence that these networks are disrupted in a dissociable fashion with regard to the functional connectivity of the thalamus and hippocampus, suggesting circuit-level dysfunction.

Encoding of 3D head direction information in the human brain

Head direction cells are critical for navigation because they convey information about which direction an animal is facing within an environment. To date, most studies on head direction encoding have been conducted on a horizontal two-dimensional (2D) plane, and little is known about how three-dimensional (3D) direction information is encoded in the brain despite humans and other animals living in a 3D world. Here, we investigated head direction encoding in the human brain while participants moved within a virtual 3D "spaceship" environment. Movement was not constrained to planes and instead participants could move along all three axes in volumetric space as if in zero gravity. Using functional magnetic resonance imaging (fMRI) multivoxel pattern similarity analysis, we found evidence that the thalamus, particularly the anterior portion, and the subiculum encoded the horizontal component of 3D head direction (azimuth). In contrast, the retrosplenial cortex was significantly more sensitive to the vertical direction (pitch) than to the azimuth. Our results also indicated that vertical direction information in the retrosplenial cortex was significantly correlated with behavioral performance during a direction judgment task. Our findings represent the first evidence showing that the "classic" head direction system that has been identified on a horizontal 2D plane also seems to encode vertical and horizontal heading in 3D space in the human brain.

Anterior thalamic nuclei, but not retrosplenial cortex, lesions abolish latent inhibition in rats

The present study examined the effects of excitotoxic lesions in 2 closely related structures, the anterior thalamic nuclei and the retrosplenial cortex, on latent inhibition. Latent inhibition occurs when nonreinforced preexposure to a stimulus retards the subsequent acquisition of conditioned responding to that stimulus. Latent inhibition was assessed in a within-subject procedure with auditory stimuli and food reinforcement. As expected, sham-operated animals were slower to acquire conditioned responding to a stimulus that had previously been experienced without consequence, relative to a non-preexposed stimulus. This latent inhibition effect was absent in rats with excitotoxic lesions in the anterior thalamic nuclei, as these animals conditioned to both stimuli at equivalent rates. The retrosplenial lesions appeared to spare latent inhibition, as these animals displayed a robust stimulus preexposure effect. The demonstration here that anterior thalamic nuclei lesions abolish latent inhibition is consistent with emerging evidence of the importance of these thalamic nuclei for attentional control. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Real-Time Readout of Large-Scale Unsorted Neural Ensemble Place Codes

Uncovering spatial representations from large-scale ensemble spike activity in specific brain circuits provides valuable feedback in closed-loop experiments. We develop a graphics processing unit (GPU)-powered population-decoding system for ultrafast reconstruction of spatial positions from rodents' unsorted spatiotemporal spiking patterns, during run behavior or sleep. In comparison with an optimized quad-core central processing unit (CPU) implementation, our approach achieves an ∼20- to 50-fold increase in speed in eight tested rat hippocampal, cortical, and thalamic ensemble recordings, with real-time decoding speed (approximately fraction of a millisecond per spike) and scalability up to thousands of channels. By accommodating parallel shuffling in real time (computation time <15 ms), our approach enables assessment of the statistical significance of online-decoded "memory replay" candidates during quiet wakefulness or sleep. This open-source software toolkit supports the decoding of spatial correlates or content-triggered experimental manipulation in closed-loop neuroscience experiments.

Striking reduction in neurons and glial cells in anterior thalamic nuclei of older patients with Down syndrome

The anterior thalamic nuclei are important for spatial and episodic memory, however, surprisingly little is known about the status of these nuclei in neurological conditions that present with memory impairments, such as Down syndrome. We quantified neurons and glial cells in the anterior thalamic nuclei of four older patients with Down syndrome. There was a striking reduction in the volume of the anterior thalamic nuclei and this appeared to reflect the loss of approximately 70% of neurons. The number of glial cells was also reduced but to a lesser degree than neurons. The anterior thalamic nuclei appear to be particularly sensitive to effects of aging in Down syndrome and the pathology in this region likely contributes to the memory impairments observed. These findings reaffirm the importance of examining the status of the anterior thalamic nuclei in conditions where memory impairments have been principally assigned to pathology in the medial temporal lobe.

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Volume of anterior thalamus is markedly reduced in older patients with Down syndrome.

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Number of neurons in anterior thalamus are substantially reduced.

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Number of glial cells in anterior thalamus are substantially reduced.

The Cognitive Thalamus as a Gateway to Mental Representations

Historically, the thalamus has been viewed as little more than a relay, simply transferring information to key players of the cast, the cortex and hippocampus, without providing any unique functional contribution. In recent years, evidence from multiple laboratories researching different thalamic nuclei has contradicted this idea of the thalamus as a passive structure. Dated models of thalamic functions are being pushed aside, revealing a greater and far more complex contribution of the thalamus for cognition. In this Viewpoints article, we show how recent data support novel views of thalamic functions that emphasize integrative roles in cognition, ranging from learning and memory to flexible adaption. We propose that these apparently separate cognitive functions may indeed be supported by a more general role in shaping mental representations. Several features of thalamocortical circuits are consistent with this suggested role, and we highlight how divergent and convergent thalamocortical and corticothalamic pathways may complement each other to support these functions. Furthermore, the role of the thalamus for subcortical integration is highlighted as a key mechanism for maintaining and updating representations. Finally, we discuss future areas of research and stress the importance of incorporating new experimental findings into existing knowledge to continue developing thalamic models. The presence of thalamic pathology in a number of neurological conditions reinforces the need to better understand the role of this region in cognition.

Increased training compensates for OX1R blockage-impairment of spatial memory and c-Fos expression in different cortical and subcortical areas

It has been suggested that the orexin system modulates learning and memory-related processes. However, the possible influence that training could have on the effect of the blockade of orexin-A selective receptor (OX1R) on a spatial memory task has not been explored. Therefore, the present study attempts to compare the effects of OX1R antagonist SB-334867 infusion on spatial memory in two different conditions in the Morris Water Maze (MWM). This experiment evaluated the animals' performance in weak training (2 trials per session) vs strong training (6 trials per session) protocols in a spatial version of the MWM. We found that in the 2-trial condition the post-training SB-334867 infusion had a negative effect on consolidation as well as on the retention and reversal learning of the task 72 h later. This effect was not apparent in the 6-trial condition. In addition, while the strong training groups showed a general increase in c-Fos expression in several brain areas of the hippocampal-thalamic-cortical circuit, SB-334867 administration had the opposite effect in areas that have been previously reported to have a high density of OX1R. Specifically, the SB-infused group in the 2-trial condition showed a decrease in c-Fos immunoreactivity in the dentate gyrus, granular retrosplenial and prelimbic cortices, and centrolateral thalamic nucleus. This was not observed for subjects in the 6-trial condition. The activation of these areas could constitute a neuroanatomical substrate involved in the compensatory mechanisms of training upon SB-334867 impairing effects on a MWM spatial task.

Do the rat anterior thalamic nuclei contribute to behavioural flexibility?

The rodent anterior thalamic nuclei (ATN) are vital for spatial memory. A consideration of their extensive frontal connections suggests that these nuclei may also subserve non-spatial functions. The current experiments explored the importance of the ATN for different aspects of behavioural flexibility, including their contribution to tasks typically associated with frontal cortex. In Experiment 1, rats with ATN lesions were tested on a series of response and visual discriminations in an operant box and, subsequently, in a water tank. The tasks included assessments of reversal learning as well switches between each discrimination dimension. Results revealed a mild and transient deficit on the operant task that was not specific to any stage of the procedure. In the water tank, the lesion animals were impaired on the reversal of a spatial discrimination but did not differ from controls on any other measure. Experiment 2 examined the impact of ATN damage on a rodent analogue of the 'Stroop', which assesses response choice during stimulus conflict. The lesion animals successfully acquired this task and were able to use contextual information to disambiguate conflicting cue information. However, responding during the initial presentation of conflicting cue information was affected by the lesion. Taken together, these results suggest that the ATN are not required for aspects of behavioural flexibility (discrimination learning, reversals or high-order switches) typically associated with the rat medial prefrontal cortex. The results from Experiment 2 suggest that the non-spatial functions of the ATN may be more aligned with those of the anterior cingulate cortex.

Dynamic Complexity of Spontaneous BOLD Activity in Alzheimer's Disease and Mild Cognitive Impairment Using Multiscale Entropy Analysis

Alzheimer's disease (AD) is characterized by progressive deterioration of brain function among elderly people. Studies revealed aberrant correlations in spontaneous blood oxygen level-dependent (BOLD) signals in resting-state functional magnetic resonance imaging (rs-fMRI) over a wide range of temporal scales. However, the study of the temporal dynamics of BOLD signals in subjects with AD and mild cognitive impairment (MCI) remains largely unexplored. Multiscale entropy (MSE) analysis is a method for estimating the complexity of finite time series over multiple time scales. In this research, we applied MSE analysis to investigate the abnormal complexity of BOLD signals using the rs-fMRI data from the Alzheimer's disease neuroimaging initiative (ADNI) database. There were 30 normal controls (NCs), 33 early MCI (EMCI), 32 late MCI (LMCI), and 29 AD patients. Following preprocessing of the BOLD signals, whole-brain MSE maps across six time scales were generated using the Complexity Toolbox. One-way analysis of variance (ANOVA) analysis on the MSE maps of four groups revealed significant differences in the thalamus, insula, lingual gyrus and inferior occipital gyrus, superior frontal gyrus and olfactory cortex, supramarginal gyrus, superior temporal gyrus, and middle temporal gyrus on multiple time scales. Compared with the NC group, MCI and AD patients had significant reductions in the complexity of BOLD signals and AD patients demonstrated lower complexity than that of the MCI subjects. Additionally, the complexity of BOLD signals from the regions of interest (ROIs) was found to be significantly associated with cognitive decline in patient groups on multiple time scales. Consequently, the complexity or MSE of BOLD signals may provide an imaging biomarker of cognitive impairments in MCI and AD.

Microstructural White Matter Abnormalities in the Dorsal Cingulum of Adolescents with IBS

Alterations in fractional anisotropy (FA) have been considered to reflect microstructural white matter (WM) changes in disease conditions; however, no study to date has examined WM changes using diffusion tensor imaging (DTI) in adolescents with irritable bowel syndrome (IBS). The objective of the present study was two-fold: (1) to determine whether differences in FA, and other non-FA metrics, were present in adolescents with IBS compared to healthy controls using whole-brain, region of interest (ROI)-restricted tract-based spatial statistics (TBSS) and canonical ROI DTI analyses for the cingulum bundle, and (2) to determine whether these metrics were related to clinical measures of disease duration and pain intensity in the IBS group. A total of 16 adolescents with a Rome III diagnosis of IBS (females = 12; mean age = 16.29, age range: 11.96-18.5 years) and 16 age- and gender-matched healthy controls (females = 12; mean age = 16.24; age range: 11.71-20.32 years) participated in this study. Diffusion-weighted images were acquired using a Siemens 3-T Trio Tim Syngo MRI scanner with a 32-channel head coil. The ROI-restricted TBSS and canonical ROI-based DTI analyses revealed that adolescents with IBS showed decreased FA in the right dorsal cingulum bundle compared to controls. No relationship between FA and disease severity measures was found. Microstructural WM alterations in the right dorsal cingulum bundle in adolescents with IBS may reflect a premorbid brain state or the emergence of a disease-driven process that results from complex changes in pain- and affect-related processing via spinothalamic and corticolimbic pathways.

Impact of putamen stroke on task context updating: Evidence from P300 brain waves

According to the context updating theory, the oddball P300 component indexes brain activities underlying revision of the mental representation induced by incoming stimuli. It involves an attention-driven comparison process that evaluates the representation of the previous event in working memory. Delayed latencies have been reported for various types of stroke such as unilateral thalamic stroke. We investigated memory updating effects in patients with putamen stroke. Two groups of patients with putamen and thalamic stroke were recruited along with two control groups of young and old healthy participants. Auditory and visual P300 were elicited respectively in a two-stimulus oddball paradigm. The auditory P300 peak latencies were significantly longer in patients with a putamen lesion than in the aged and young control groups and the same pattern was found in the thalamus-lesioned patient. The delayed auditory P300 component in both patient groups but neither control group suggests impairment of memory updating in patients with putamen stroke comparable with thalamic stroke. Our study illustrates the important role of subcortical structures subserved in context updating.

Deep brain stimulation for seizure control in drug-resistant epilepsy

Antiepileptic drugs prevent morbidity and death in a large number of patients suffering from epilepsy. However, it is estimated that approximately 30% of epileptic patients will not have adequate seizure control with medication alone. Resection of epileptogenic cortex may be indicated in medically refractory cases with a discrete seizure focus in noneloquent cortex. For patients in whom resection is not an option, deep brain stimulation (DBS) may be an effective means of seizure control. Deep brain stimulation targets for treating seizures primarily include the thalamic nuclei, hippocampus, subthalamic nucleus, and cerebellum. A variety of stimulation parameters have been studied, and more recent advances in electrical stimulation to treat epilepsy include responsive neurostimulation. Data suggest that DBS is effective for treating drug-resistant epilepsy.

Neuroimaging in the Kleine-Levin Syndrome

PURPOSE OF REVIEW

The purpose was to review the most recent literature on neuroimaging in the Kleine-Levin syndrome (KLS). We aimed to investigate if frontotemporal and thalamic dysfunction are key KLS signatures, and if recent research indicates other brain networks of interest that elucidate KLS symptomatology and aetiology.

RECENT FINDINGS

In a comprehensive literature search, we found 12 original articles published 2013-2018. Most studies report deviations related to cerebral perfusion, glucose metabolism, or blood-oxygen-level-dependent responses in frontotemporal areas and/or the thalamus. Studies also report dysfunction in the temporoparietal junction and the oculomotor network that also were related to clinical parameters. We discuss these findings based on recent research on thalamocortical networks and brain stem white matter tracts. The hypothesis of frontotemporal and thalamic involvement in KLS was confirmed, and additional findings in the temporoparietal junction and the oculomotor system suggest a broader network involvement, which can be investigated by future high-resolution and multimodal imaging.

Rethinking schizophrenia through the lens of evolution: shedding light on the enigma

Schizophrenia refers to a complex psychiatric illness characterized by the heterogenic presence of positive, negative and cognitive symptoms occurring in all human societies. The fact that the disorder lacks a unifying neuropathology, presents a decreased fecundity of the affected individuals and has a cross-culturally stable incidence rate, makes it necessary for an evolutionary explanation that fully accounts for the preservation of “schizophrenic genes” in the global human genepool, explaining the potential sex differences and the heterogeneous cognitive symptomatology of the disorder and is consistent with the neuropsychological, developmental and evolutionary findings regarding the human brain. Here we proposed a new evolutionary framework for schizophrenia that is consistent with findings presented in different dimensions, considering the disorder as a form of brain functioning that allows us to adapt to the environment and, ultimately, maintain the survival of the species. We focus on the epigenetic regulation of thalamic interneurons as a major player involved in the development of the clinical picture characteristic of schizophrenia.

SPG11 mutations cause widespread white matter and basal ganglia abnormalities, but restricted cortical damage

SPG11 mutations are the major cause of autosomal recessive Hereditary Spastic Paraplegia. The disease has a wide phenotypic variability indicating many regions of the nervous system besides the corticospinal tract are affected. Despite this, anatomical and phenotypic characterization is restricted. In the present study, we investigate the anatomical abnormalities related to SPG11 mutations and how they relate to clinical and cognitive measures. Moreover, we aim to depict how the disease course influences the regions affected, unraveling different susceptibility of specific neuronal populations. We performed clinical and paraclinical studies encompassing neuropsychological, neuroimaging, and neurophysiological tools in a cohort of twenty-five patients and age matched controls. We assessed cortical thickness (FreeSurfer software), deep grey matter volumes (T1-MultiAtlas tool), white matter microstructural damage (DTI-MultiAtlas) and spinal cord morphometry (Spineseg software) on a 3 T MRI scan. Mean age and disease duration were 29 and 13.2 years respectively. Sixty-four percent of the patients were wheelchair bound while 84% were demented. We were able to unfold a diffuse pattern of white matter integrity loss as well as basal ganglia and spinal cord atrophy. Such findings contrasted with a restricted pattern of cortical thinning (motor, limbic and parietal cortices). Electromyography revealed motor neuronopathy affecting 96% of the probands. Correlations with disease duration pointed towards a progressive degeneration of multiple grey matter structures and spinal cord, but not of the white matter. SPG11-related hereditary spastic paraplegia is characterized by selective neuronal vulnerability, in which a precocious and widespread white matter involvement is later followed by a restricted but clearly progressive grey matter degeneration.

Role of retrosplenial cortex in processing stress-related context memories

This work summarizes evidence for the role of RSC in processing fear-inducing context memories. Specifically, we discuss molecular, cellular, and network mechanisms by which RSC might contribute the processing of contextual fear memories. We focus on glutamatergic and cholinergic mechanisms underlying encoding, retrieval, and extinction of context-dependent fear. RSC mechanisms underlying retrieval of recently and remotely acquired memories are compared to memory mechanisms of anterior cortices. Due to the strong connectivity between hippocampus and RSC, we also compare the extent to which their mechanisms of encoding, retrieval, and extinction show overlap. At a theoretical level, we discuss the role of RSC in the framework of systems consolidation as well as retrieval-induced memory modulation. Lastly, we emphasize the implication of these findings for psychopathologies associated with neurological and psychiatric disorders. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Executive Functions May Predict Outcome in Deep Brain Stimulation of Anterior Nucleus of Thalamus for Treatment of Refractory Epilepsy

Background

Deep brain stimulation (DBS) of the anterior nucleus of thalamus (ANT) is an emerging treatment option for patients suffering from refractory epilepsy. ANT has extensive connections with hippocampus and retrosplenial cingulum, areas associated mainly with spatial memory and with anterior cingulum which is important in executive functions. As refractory epilepsy is often associated with cognitive decline and neuronal damage, the decreased connectivity between ANT and remote structures might impact on the effects of DBS.

Objective

We hypothesized that the neuropsychological profile could reflect the connectivity of ANT and further predict the efficacy of ANT DBS. We evaluated the cognitive performance of patients with refractory epilepsy with DBS to evaluate whether neuropsychological profiles could reflect the connectivity of ANT and further predict the efficacy of ANT DBS.

Method

Sixteen patients with refractory epilepsy treated with ANT DBS with at least 2 years of follow-up were included in the study. Patients underwent a neuropsychological evaluation as a part of the protocol and their clinical outcome was determined by seizure frequency in the last 6 months compared to baseline. The patients were classified as responders if there was a ≥50% reduction in the frequency of the predominant seizure type, otherwise as nonresponders.

Results

There were 12 responders and 4 nonresponders for ANT DBS treatment in the study population. Nonresponders performed worse than responders in neuropsychological tasks measuring executive functions and attention, such as the Trail-Making Test.

Conclusion

Better executive functions and attention seemed to predict improved clinical outcome after the ANT DBS surgery. Based on our preliminary descriptive findings and the anatomical connectivity hypothesis, we suggest that deficits in executive functions may relate to an inferior outcome. This finding might offer new tools for refining the selection of patients with refractory epilepsy scheduled to undergo ANT DBS surgery. Moreover, it highlights the need for further investigations of neural connectivity in epilepsy.

Dissociating Landmark Stability from Orienting Value Using Functional Magnetic Resonance Imaging

Retrosplenial cortex (RSC) plays a role in using environmental landmarks to help orientate oneself in space. It has also been consistently implicated in processing landmarks that remain fixed in a permanent location. However, it is not clear whether the RSC represents the permanent landmarks themselves or instead the orienting relevance of these landmarks. In previous functional magnetic resonance imaging (fMRI) studies, these features have been conflated-stable landmarks were always useful for orienting. Here, we dissociated these two key landmark attributes to investigate which one best reflects the function of the RSC. Before scanning, participants learned the features of novel landmarks about which they had no prior knowledge. During fMRI scanning, we found that the RSC was more engaged when people viewed permanent compared with transient landmarks and was not responsive to the orienting relevance of landmarks. Activity in RSC was also related to the amount of landmark permanence information a person had acquired and, as knowledge increased, the more the RSC drove responses in the anterior thalamus while viewing permanent landmarks. In contrast, the angular gyrus and the hippocampus were engaged by the orienting relevance of landmarks, but not their permanence, with the hippocampus also sensitive to the distance between relevant landmarks and target locations. We conclude that the coding of permanent landmarks in RSC may drive processing in regions like anterior thalamus, with possible implications for the efficacy of functions such as navigation.

Thalamic functional connectivity and its association with behavioral performance in older age

Introduction

Despite the thalamus' dense connectivity with both cortical and subcortical structures, few studies have specifically investigated how thalamic connectivity changes with age and how such changes are associated with behavior. This study investigated the effect of age on thalamo-cortical and thalamo-hippocampal functional connectivity (FC) and the association between thalamic FC and visual-spatial memory and reaction time (RT) performance in older adults.

Methods

Resting-state functional magnetic resonance images were obtained from younger (n = 20) and older (n = 20) adults. A seed-based approach was used to assess the FC between the thalamus and (1) sensory resting-state networks; (2) the hippocampus. Participants also completed visual-spatial memory and RT tasks, from the Cambridge Neuropsychological Test Automated Battery (CANTAB).

Results

Older adults exhibited a loss of specificity in the FC between sensory thalamic subregions and corresponding sensory cortex. Greater thalamo-motor FC in older adults was associated with faster RTs. Furthermore, older adults exhibited greater thalamo-hippocampal FC compared to younger adults, which was greatest for those with the poorest visual-spatial memory performance.

Conclusion

Although older adults exhibited poorer visual-spatial memory and slower reaction times compared to younger adults, "good" and "poorer" older performers exhibited different patterns of thalamo-cortical and thalamo-hippocampal FC. These results highlight the potential role of thalamic connectivity in supporting reaction times and memory in aging. Furthermore, these results highlight the importance of including the thalamus in studies of aging to fully understand how brain changes with age may be associated with behavior.

A Structural Connectivity Approach to Validate a Model-based Technique for the Segmentation of the Pulvinar Complex

The pulvinar of the thalamus is a higher-order thalamic nucleus that is responsible for gating information flow to the cortical regions of the brain. It is involved in several cortico-thalamocortical relay circuits and is known to be affected in a number of neurological disorders. Segmenting the pulvinar in clinically acquired images is important to support studies exploring its role in brain function. In recent years, we have proposed an active shape model method to segment multiple thalamic nuclei, including the pulvinar. The model was created by manual delineation of high resolution 7T images and the process was guided by the Morel stereotactic atlas. However, this model is based on a small library of healthy subjects, and it is important to validate the reliability of the segmentation method on a larger population of clinically acquired images. The pulvinar is known to have particularly strong white matter connections to the hippocampus, which allows us to identify the pulvinar from thalamic regions of high hippocampal structural connectivity. In this study, we obtained T1-weighted and diffusion MR data from 43 healthy volunteers using a clinical 3T MRI scanner. We applied the segmentation method to the T1-weighted images to obtain the intrathalamic nuclei, and we calculated the connectivity maps between the hippocampus and thalamus using the diffusion images. Our results show that the shape model segmentation consistently localizes the pulvinar in the region with the highest hippocampal connectivity. The proposed method can be extended to other nuclei to further validate our segmentation method.

Influences of photic stress on postsubicular head-directional processing

The stress response serves vital adaptive functions. However, acute stress episodes often negatively impact cognitive processing. Here, we aimed to elucidate whether stress detrimentally affects the head‐direction cells of the postsubiculum, which may in turn impair downstream spatial information processing. We recorded neurons in the rats’ postsubiculum during a pellet‐chasing task during baseline non‐stress conditions and after a 30‐min acute photic stress exposure. Based on their baseline firing rate, we identified a subpopulation of head‐direction cells that drastically decreased its firing rate as a response to stress while preserving their head directionality. The remaining population of head‐direction cells as well as other neurons recorded in the postsubiculum were unaffected. The observed altered activity in the subpopulation might be the basis for spatial processing deficits observed following acute stress episodes.

Pseudoexfoliation syndrome without glaucoma: White matter abnormalities detected by conventional MRI and diffusion tensor imaging

PURPOSE

To assess macro- and microstructural brain changes in patients with pseudoexfoliation syndrome (PXS).

MATERIALS AND METHODS

Comprehensive ophthalmic examination and brain MRI were conducted on 20 patients with PXS without glaucoma (aged 62.75 ± 0.4 years) and 20 controls (aged 62 ± 0.6 years). White matter (WM) integrity was evaluated on FLAIR and single-shot multisection SE-EPI diffusion tensor imaging (DTI) sequences. The presence and the number of white matter hyperintensities (WMHIs) on FLAIR images was compared between all patients and control subjects. Microstructural WM changes on DTI was evaluated using Tract-based spatial statistics (TBSS). DTI metrics of the optic tracts were assessed by the region-of-interest (ROI) method.

RESULTS

A significantly higher number of WMHIs was found in the patients with PXS than in the control subjects (P ≤ 0.002). On DTI the patients showed bilateral increase in the mean diffusivity (MD), axial diffusivity (AD) and radial diffusivity (RD) values in the anterior thalamic radiation, the inferior fronto-occipital fasciculus, the superior longitudinal fasciculus, the inferior longitudinal fasciculus and the forceps minor. TBSS revealed no significant difference in fractional anisotropy (FA) values, but ROIs analysis of the optic tracts revealed decreased FA values in the patients.

CONCLUSION

MRI in patients with PXS detects abnormalities in the brain and the optic tracts at a subclinical stage. Early detection of microstructural changes could be useful to guide appropriate treatment to impede the disease process.

Involvement of the Avian Dorsal Thalamic Nuclei in Homing Pigeon Navigation

The navigational ability of birds has been a focus of popular and scientific interest for centuries, but relatively little is known about the neuronal networks that support avian navigation. In the brain, regions like the piriform cortex, olfactory bulbs, hippocampal formation, vestibular nuclei, and the wulst, are among the brain regions often discussed as involved in avian navigation. However, despite large literature showing a prominent role of some anterior and dorsal thalamic nuclei in mammalian spatial navigation, little is known about the role of the thalamus in avian navigation. Here, we analyzed a possible role of the dorsal anterior thalamic nuclei in avian navigation by combining olfactory manipulations during the transport of young homing pigeons to a release site and c-Fos immunohistochemistry for the mapping brain activity. The results reveal that odor modulated neurons in the avian dorsolateral lateral (DLL) subdivision of the anterior thalamic nuclei are actively involved in processing outward journey, navigational information. Outward journey information is used by pigeons to correctly determine the homeward direction. DLL participation in acquiring path-based information, and its modulation by olfactory exposure, broadens our understanding of the neural pathways underlying avian navigation.

Increased Hippocampal ProBDNF Contributes to Memory Impairments in Aged Mice

Memory decline during aging or accompanying neurodegenerative diseases, represents a major health problem. Neurotrophins have long been considered relevant to the mechanisms of aging-associated cognitive decline and neurodegeneration. Mature Brain-Derived Neurotrophic Factor (BDNF) and its precursor (proBDNF) can both be secreted in response to neuronal activity and exert opposing effects on neuronal physiology and plasticity. In this study, biochemical analyses revealed that increased levels of proBDNF are present in the aged mouse hippocampus relative to young and that the level of hippocampal proBDNF inversely correlates with the ability to perform in a spatial memory task, the water radial arm maze (WRAM). To ascertain the role of increased proBDNF levels on hippocampal function and memory we performed infusions of proBDNF into the CA1 region of the dorsal hippocampus in male mice trained in the WRAM paradigm: In well-performing aged mice, intra-hippocampal proBDNF infusions resulted in a progressive and significant impairment of memory performance. This impairment was associated with increased p-cofilin levels, an important regulator of dendritic spines and synapse physiology. On the other hand, in poor performers, intra-hippocampal infusions of TAT-Pep5, a peptide which blocks the interaction between the p75 Neurotrophin Receptor (p75NTR) and RhoGDI, significantly improved learning and memory, while saline infusions had no effect. Our results support a role for proBDNF and its receptor p75NTR in aging-related memory impairments.

Neural correlates of visual memory in patients with diffuse axonal injury

PRIMARY OBJECTIVE

To investigate the neural substrates of visual memory in a sample of patients with traumatic brain injury (TBI). We hypothesized that patients with decreased grey and white matter volume in frontal and parietal cortices as well as medial temporal and occipital lobes would perform poorly on the tests of visual memory analysed.

METHODS AND PROCEDURES

39 patients and 53 controls were assessed on tests of visual memory and learning from the Cambridge Neuropsychological Test Automated Battery (CANTAB). Patients with TBI were scanned with magnetic resonance imaging (MRI). Partial correlations and multiple regression analyses were used to examine relationships between cognitive variables and MRI volumetric findings. This study complements and extends previous studies by performing volumetric comparisons on a variety of resolution levels, from whole brain to voxel-based level analysis.

MAIN OUTCOMES AND RESULTS

Patients with TBI performed significantly worse than controls in all the tasks assessed. Performance was associated with wide-spread reductions in grey and white matter volume of several cortical and subcortical structures as well as with cerebrospinal fluid space enlargement in accordance with previous studies of memory in patients with TBI and cognitive models suggesting that memory problems involve the alteration of multiple systems.

CONCLUSIONS

Our results propose that compromised visual memory in patients with TBI is related to a distributed pattern of volume loss in regions mediating memory and attentional processing.

Neurodegeneration and NLRP3 inflammasome expression in the anterior thalamus of SOD1(G93A) ALS mice

Nowadays, amyotrophic lateral sclerosis (ALS) is considered as a multisystem disorder, characterized by a primary degeneration of motor neurons as well as neuropathological changes in non-motor regions. Neurodegeneration in subcortical areas, such as the thalamus, are believed to contribute to cognitive and behavioral abnormalities in ALS patients. In the present study, we investigated neurodegenerative changes including neuronal loss and glia pathology in the anterodorsal thalamic nucleus (AD) of SOD1(G93A) mice, a widely used animal model for ALS. We detected massive dendrite swelling and neuronal loss in SOD1(G93A) animals, which was accompanied by a mild gliosis. Furthermore, misfolded SOD1 protein and autophagy markers were accumulating in the AD. Since innate immunity and activation inflammasomes seem to play a crucial role in ALS, we examined protein expression of Nod-like receptor protein 3 (NLRP3), apoptosis-associated speck-like protein containing a caspase-1 recruitment domain (ASC) and the cytokine interleukin 1 beta (IL1β) in AD glial cells and neurons. NLRP3 and ASC were significantly up-regulated in the AD of SOD1(G93A) mice. Finally, co-localization studies revealed expression of NLRP3, ASC and IL1β in neurons. Our study yielded two main findings: (i) neurodegenerative changes already occur at an early symptomatic stage in the AD and (ii) increased inflammasome expression may contribute to neuronal cell death. In conclusion, neurodegeneration in the anterior thalamus may critically account for cognitive changes in ALS pathology.

Asymmetric cross-hemispheric connections link the rat anterior thalamic nuclei with the cortex and hippocampal formation

Dense reciprocal connections link the rat anterior thalamic nuclei with the prelimbic, anterior cingulate and retrosplenial cortices, as well as with the subiculum and postsubiculum. The present study compared the ipsilateral thalamic-cortical connections with the corresponding crossed, contralateral connections between these same sets of regions. All efferents from the anteromedial thalamic nucleus to the cortex, as well as those to the subiculum, remained ipsilateral. In contrast, all of these target sites provided reciprocal, bilateral projections to the anteromedial nucleus. While the anteroventral thalamic nucleus often shared this same asymmetric pattern of cortical connections, it received relatively fewer crossed inputs than the anteromedial nucleus. This difference was most marked for the anterior cingulate projections, as those to the anteroventral nucleus remained almost entirely ipsilateral. Unlike the anteromedial nucleus, the anteroventral nucleus also appeared to provide a restricted, crossed projection to the contralateral retrosplenial cortex. Meanwhile, the closely related laterodorsal thalamic nucleus had almost exclusively ipsilateral efferent and afferent cortical connections. Likewise, within the hippocampus, the postsubiculum seemingly had only ipsilateral efferent and afferent connections with the anterior thalamic and laterodorsal nuclei. While the bilateral cortical projections to the anterior thalamic nuclei originated predominantly from layer VI, the accompanying sparse projections from layer V largely gave rise to ipsilateral thalamic inputs. In testing a potentially unifying principle of anterior thalamic - cortical interactions, a slightly more individual pattern emerged that reinforces other evidence of functional differences within the anterior thalamic and also helps to explain the consequences of unilateral interventions involving these nuclei.

Spatial Navigation and the Central Complex: Sensory Acquisition, Orientation, and Motor Control

Cockroaches are scavengers that forage through dark, maze-like environments. Like other foraging animals, for instance rats, they must continually asses their situation to keep track of targets and negotiate barriers. While navigating a complex environment, all animals need to integrate sensory information in order to produce appropriate motor commands. The integrated sensory cues can be used to provide the animal with an environmental and contextual reference frame for the behavior. To successfully reach a goal location, navigational cues continuously derived from sensory inputs have to be utilized in the spatial guidance of motor commands. The sensory processes, contextual and spatial mechanisms, and motor outputs contributing to navigation have been heavily studied in rats. In contrast, many insect studies focused on the sensory and/or motor components of navigation, and our knowledge of the abstract representation of environmental context and spatial information in the insect brain is relatively limited. Recent reports from several laboratories have explored the role of the central complex (CX), a sensorimotor region of the insect brain, in navigational processes by recording the activity of CX neurons in freely-moving insects and in more constrained, experimenter-controlled situations. The results of these studies indicate that the CX participates in processing the temporal and spatial components of sensory cues, and utilizes these cues in creating an internal representation of orientation and context, while also directing motor control. Although these studies led to a better understanding of the CX's role in insect navigation, there are still major voids in the literature regarding the underlying mechanisms and brain regions involved in spatial navigation. The main goal of this review is to place the above listed findings in the wider context of animal navigation by providing an overview of the neural mechanisms of navigation in rats and summarizing and comparing our current knowledge on the CX's role in insect navigation to these processes. By doing so, we aimed to highlight some of the missing puzzle pieces in insect navigation and provide a different perspective for future directions.

Korsakoff's syndrome: a critical review

In this review, we present a survey on Korsakoff's syndrome (KS), a residual syndrome in patients who suffered from a Wernicke encephalopathy (WE) that is predominantly characterized by global amnesia, and in more severe cases also by cognitive and behavioral dysfunction. We describe the history of KS and its definition, its epidemiology, and the lack of consensus criteria for its diagnosis. The cognitive and behavioral symptoms of KS, which include anterograde and retrograde amnesia, executive dysfunction, confabulation, apathy, as well as affective and social-cognitive impairments, are discussed. Moreover, recent insights into the underlying neurocognitive mechanisms of these symptoms are presented. In addition, the evidence so far on the etiology of KS is examined, highlighting the role of thiamine and alcohol and discussing the continuity hypothesis. Furthermore, the neuropathology of KS is reviewed, focusing on abnormalities in the diencephalon, including the mammillary bodies and thalamic nuclei. Pharmacological treatment options and nonpharmacological interventions, such as those based on cognitive rehabilitation, are discussed. Our review shows that thiamine deficiency (TD) is a crucial factor in the etiology of KS. Although alcohol abuse is by far the most important context in which TD occurs, there is no convincing evidence for an essential contribution of ethanol neurotoxicity (EN) to the development of WE or to the progression of WE to KS. Future research on the postmortem histopathological analysis of brain tissues of KS patients is crucial for the advancement of our knowledge of KS, especially for associating its symptoms with lesions in various thalamic nuclei. A necessary requirement for the advancement of studies on KS is the broad acceptance of a comprehensive definition and definite diagnostic criteria. Therefore, in this review, we propose such a definition of KS and draft outlines for prospective diagnostic criteria.

Medio-dorsal thalamus and confabulations: Evidence from a clinical case and combined MRI/DTI study

The Medio-Dorsal Nuclei (MDN) including the thalamic magnocellular and parvocellular thalamic regions has been implicated in verbal memory function. In a 77 year old lady, with a prior history of a clinically silent infarct of the left MDN, we observed the acute onset of spontaneous confabulations when an isolated new infarct occurred in the right MDN. The patient and five age-matched healthy subjects underwent Magnetic Resonance Imaging (MRI) and Diffusion Tensor Imaging (DTI). The thalamic lesions were localized by overlapping Morel Thalamic Atlas with structural MRI data. DTI was used to assess: i) white matter alterations (Fractional Anisotropy, FA) within fibers connecting the ischemic areas to cortex; ii) the micro-structural damage (Mean Diffusivity) within the thalamic sub-regions defined by their structural connectivity to the Anterior Cingulate Cortex (ACC) and to the temporal lobes. These target regions were chosen because their damage is considered associated with the appearance of confabulations. Thalamic lesions were localized within the parvocellular regions of the right and left MDNs. The structural connectivity study showed that the fiber tracts, connecting the bilaterally damaged thalamic regions with the frontal cortex, corresponded to the anterior thalamic radiations (ATR). FA within these tracts was significantly lower in the patient as compared to controls. Mean diffusivity within the MDNs projecting to Broadman area (BA) 24, BA25 and BA32 of ACC was significantly higher in the patient than in control group. Mean diffusivity values within the MDN projecting to temporal lobes in contrast were not different between patient and controls. Our findings suggest the involvement of bilateral MDNs projections to ACC in the genesis of confabulations and help provide clarity to the longstanding debate on the origin of confabulations.

Hippocampal shape alterations are associated with regional Aβ load in cognitively normal elderly individuals

Aβ deposition is a driving force of Alzheimer's disease pathology and can be detected early by amyloid positron emission tomography. Identifying presymptomatic structural brain changes associated with Aβ deposition might lead to a better understanding of its consequences and provide early diagnostic information. In this respect we analyzed measures of cortical thickness and subcortical volumes along with hippocampal, thalamic and striatal shape and surface area by applying novel analysis strategies for structural magnetic resonance imaging. We included 69 cognitively normal elderly subjects after careful clinical and neuropsychological workup. Standardized uptake value ratios (cerebellar reference) for uptake of 11-C-Pittsburgh Compound B (PiB) were calculated from positron emission tomographic data for a cortical measurement and for bilateral hippocampus, thalamus and striatum. Associations to shape, surface area, volume and cortical thickness were tested using regression models that included significant predictors as covariates. Left anterior hippocampal shape was associated with regional PiB uptake (P < 0.05, FDR corrected), whereas volumes of the hippocampi and their subregions were not associated with cortical or regional PiB uptake (all P > 0.05, FDR corrected). Within the entorhinal cortical region of both hemispheres, thickness was negatively associated with cortical PiB uptake (P < 0.05, FDR corrected). Hence, localized shape measures and cortical thickness may be potential biomarkers of presymptomatic Alzheimer's disease.

Thalamic Shape and Cognitive Performance in Amnestic Mild Cognitive Impairment

OBJECTIVE

This study aimed to investigate thalamic shape alterations and their relationships with various episodic memory impairments in subjects with amnestic mild cognitive impairment (aMCI).

METHODS

We compared volumes and morphological alterations of the thalamus between aMCI subjects and healthy controls. In addition, we investigated the correlation between thalamic deformations and various memory impairments in aMCI subjects using a comprehensive neuropsychological battery.

RESULTS

The normalized left thalamic volumes of the aMCI group were significantly smaller than those of the healthy control group (p<0.0001). aMCI subjects exhibited significant thalamic deformations in the left thalamic dorso-medial and antero-medial areas compared with healthy individuals. CERAD-K Word List Memory scores were significantly correlated with the left dorso-medial areas in aMCI subjects. There were no significant correlations between verbal fluency, Boston naming test, constructional praxis, Word List Recognition, and Visuospatial Recall scores and thalamic shape in aMCI subjects. Verbal delayed recall scores were also significantly correlated with the left dorso-medial areas in the aMCI group.

CONCLUSION

Structural alterations in the thalamic deformations in the left dorso-medial and antero-medial areas might be core underlying neurobiological mechanisms of thalamic dysfunction related to Word List Memory and delayed verbal recall in individuals with aMCI.