Thalamic System Research Articles

Where Do Core Thalamocortical Axons Terminate in Mammalian Neocortex When There Is No Cytoarchitecturally Distinct Layer 4?

Although the mammalian cerebral cortex is most often described as a hexalaminar structure, there are cortical areas (primary motor cortex) and species (elephants, cetaceans, and hippopotami), where a cytoarchitecturally indistinct, or absent, layer 4 is noted. Thalamocortical projections from the core, or first order, thalamic system terminate primarily in layers 4/inner 3. We explored the termination sites of core thalamocortical projections in cortical areas and in species where there is no cytoarchitecturally distinct layer 4 using the immunolocalization of vesicular glutamate transporter 2, a known marker of core thalamocortical axon terminals, in 31 mammal species spanning the eutherian radiation. Several variations from the canonical cortical column outline of layer 4 and core thalamocortical inputs were noted. In shrews/microchiropterans, layer 4 was present, but many core thalamocortical projections terminated in layer 1 in addition to layers 4 and inner 3. In primate primary visual cortex, the sublaminated layer 4 was associated with a specialized core thalamocortical projection pattern. In primate primary motor cortex, no cytoarchitecturally distinct layer 4 was evident and the core thalamocortical projections terminated throughout layer 3. In the African elephant, cetaceans, and river hippopotamus, no cytoarchitecturally distinct layer 4 was observed and core thalamocortical projections terminated primarily in inner layer 3 and less densely in outer layer 3. These findings are contextualized in terms of cortical processing, perception, and the evolutionary trajectory leading to an indistinct or absent cortical layer 4.

Obsessive-compulsive disorder after traumatic brain injury: case report.

IntroductionAlthough not the most prevalent clinical presentation, obsessive compulsive (OC) symptoms have been reported after TBI. Post-TBI OC disorder (OCD) cases are rare, so that OC symptoms in this setting are frequently described as OC personality disorders (OCPD).Generally, the clinical features of post-TBI OCD are thought to be similar to those observed in idiopathic OCD, assuming the probable involvement of structures such as the orbitofrontal cortex, basal ganglia, limbic and thalamic systems in its pathophysiology, although no anatomical location clearly associated with post-TBI OCD being recognized.ObjectivesBrief systematic review of OCD post-TBI and case report.MethodsBibliographic research using Pubmed. Clinical interviews and file consultation, with patient informed consent.ResultsWe present a case of a 63-year-old patient referred to the Psychiatry Consultation due to obsessive thoughts of dirt and contamination, accompanied by compulsive cleaning and sanitizing behaviors with at least 3 years of evolution with a history of TBI and right frontopolar hemorrhage 5 years ago. These behaviors significantly impaired his functionality (cleaning objects on average 300 to 700 times a day, spending hours in the shower). The patient had insight for the excessive behaviors and its daily impairment.ConclusionsPsychopathology in the post-TBI context is not infrequent, however reported cases of post-TBI OCD are described as rare in the current literature. The short description of this phenomenon implies the need for more studies focused on the study of the phenomenology of post-TBI OCD. For example, while OCD and obsessive-compulsive symptoms tend to be recognizable psychiatric phenomena, neurobehavioral sequelae in a post-TBI context can present multiple manifestations and resemble OC phenomena, without actually constituting OCD.Disclosure of InterestNone Declared

Cognitive Improvement via Left Angular Gyrus-Navigated Repetitive Transcranial Magnetic Stimulation Inducing the Neuroplasticity of Thalamic System in Amnesic Mild Cognitive Impairment Patients.

Stimulating superficial brain regions highly associated with the hippocampus by repetitive transcranial magnetic stimulation (rTMS) may improve memory of Alzheimer's disease (AD) spectrum patients. We recruited 16 amnesic mild cognitive impairment (aMCI) and 6 AD patients in the study. All the patients were stimulated to the left angular gyrus, which was confirmed a strong link to the hippocampus through neuroimaging studies, by the neuro-navigated rTMS for four weeks. Automated fiber quantification using diffusion tensor imaging metrics and graph theory analysis on functional network were employed to detect the neuroplasticity of brain networks. After neuro-navigated rTMS intervention, the episodic memory of aMCI patients and Montreal Cognitive Assessment score of two groups were significantly improved. Increased FA values of right anterior thalamic radiation among aMCI patients, while decreased functional network properties of thalamus subregions were observed, whereas similar changes not found in AD patients. It is worth noting that the improvement of cognition was associated with the neuroplasticity of thalamic system. We speculated that the rTMS intervention targeting left angular gyrus may be served as a strategy to improve cognitive impairment at the early stage of AD patients, supporting by the neuroplasticity of thalamic system.

Basal Ganglia and Thalamic Contributions to Language Function: Insights from A Parallel Distributed Processing Perspective.

Cerebral representations are encoded as patterns of activity involving billions of neurons. Parallel distributed processing (PDP) across these neuronal populations provides the basis for a number of emergent properties: 1) processing occurs and knowledge (long term memories) is stored (as synaptic connection strengths) in exactly the same networks; 2) networks have the capacity for setting into stable attractor states corresponding to concepts, symbols, implicit rules, or data transformations; 3) networks provide the scaffold for the acquisition of knowledge but knowledge is acquired through experience; 4) PDP networks are adept at incorporating the statistical regularities of experience as well as frequency and age of acquisition effects; 5) networks enable content-addressable memory; 6) because knowledge is distributed throughout networks, they exhibit the property of graceful degradation; 7) networks intrinsically provide the capacity for inference. This paper details the features of the basal ganglia and thalamic systems (recurrent and distributed connectivity) that support PDP. The PDP lens and an understanding of the attractor trench dynamics of the basal ganglia provide a natural explanation for the peculiar dysfunctions of Parkinson's disease and the mechanisms by which dopamine deficiency is causal. The PDP lens, coupled with the fact that the basal ganglia of humans bears strong homology to the basal ganglia of lampreys and the central complex of arthropods, reveals that the fundamental function of the basal ganglia is computational and involves the reduction of the vast dimensionality of a complex multi-dimensional array of sensorimotor input into the optimal choice from a small repertoire of behavioral options - the essence of reactive intention (automatic responses to sensory input). There is strong evidence that the sensorimotor basal ganglia make no contributions to cognitive or motor function in humans but can cause serious dysfunction when pathological. It appears that humans, through the course of evolution, have developed cortical capacities (working memory and volitional and reactive attention) for managing sensory input, however complex, that obviate the need for the basal ganglia. The functions of the dorsal tier thalamus, however, even viewed with an understanding of the properties of population encoded representations, remain somewhat more obscure. Possibilities include the enabling of attractor state constellations that optimize function by taking advantage of simultaneous input from multiple cortical areas; selective engagement of cortical representations; and support of the gamma frequency synchrony that enables binding of the multiple network representations that comprise a full concept representation.

Organization of primate amygdalar-thalamic pathways for emotions.

Studies on the thalamus have mostly focused on sensory relay nuclei, but the organization of pathways associated with emotions is not well understood. We addressed this issue by testing the hypothesis that the primate amygdala acts, in part, like a sensory structure for the affective import of stimuli and conveys this information to the mediodorsal thalamic nucleus, magnocellular part (MDmc). We found that primate sensory cortices innervate amygdalar sites that project to the MDmc, which projects to the orbitofrontal cortex. As in sensory thalamic systems, large amygdalar terminals innervated excitatory relay and inhibitory neurons in the MDmc that facilitate faithful transmission to the cortex. The amygdala, however, uniquely innervated a few MDmc neurons by surrounding and isolating large segments of their proximal dendrites, as revealed by three-dimensional high-resolution reconstruction. Physiologic studies have shown that large axon terminals are found in pathways issued from motor systems that innervate other brain centers to help distinguish self-initiated from other movements. By analogy, the amygdalar pathway to the MDmc may convey signals forwarded to the orbitofrontal cortex to monitor and update the status of the environment in processes deranged in schizophrenia, resulting in attribution of thoughts and actions to external sources.

S169 Sleep spindles and epilepsy

Sleep spindles (SSPs) are well known EEG phenomena characteristic to slow wave sleep (SWS). It has been demonstrated that SSPs participate in memory consolidation process during sleep. There are evidences of the participation of SSPs in various types of epilepsy ranging from idiopathic generalized to focal ones. Here we report the results of our investigation in human focal epilepsy patients implanted with cortical and thalamic macro-, and microelectrodes. Intracortical generators of SSPs in humans were explored and participation of different thalamic output systems was hypothesized. We review the human thalamic recordings and the participation of different thalamic nuclei in sleep spindling. We report our results from anterior nucleus of thalamus in temporal lobe epilepsy patients. We draw conclusions about the altered role of SSPs in the epileptogenic process.

Midline thalamic neurons are differentially engaged during hippocampus network oscillations

The midline thalamus is reciprocally connected with the medial temporal lobe, where neural circuitry essential for spatial navigation and memory formation resides. Yet, little information is available on the dynamic relationship between activity patterns in the midline thalamus and medial temporal lobe. Here, we report on the functional heterogeneity of anatomically-identified thalamic neurons and the differential modulation of their activity with respect to dorsal hippocampal rhythms in the anesthetized mouse. Midline thalamic neurons expressing the calcium-binding protein calretinin, irrespective of their selective co-expression of calbindin, discharged at overall low levels, did not increase their activity during hippocampal theta oscillations, and their firing rates were inhibited during hippocampal sharp wave-ripples. Conversely, thalamic neurons lacking calretinin discharged at higher rates, increased their activity during hippocampal theta waves, but remained unaffected during sharp wave-ripples. Our results indicate that the midline thalamic system comprises at least two different classes of thalamic projection neuron, which can be partly defined by their differential engagement by hippocampal pathways during specific network oscillations that accompany distinct behavioral contexts. Thus, different midline thalamic neuronal populations might be selectively recruited to support distinct stages of memory processing, consistent with the thalamus being pivotal in the dialogue of cortical circuits.

Control of Somatosensory Cortical Processing by Thalamic Posterior Medial Nucleus: A New Role of Thalamus in Cortical Function.

Current knowledge of thalamocortical interaction comes mainly from studying lemniscal thalamic systems. Less is known about paralemniscal thalamic nuclei function. In the vibrissae system, the posterior medial nucleus (POm) is the corresponding paralemniscal nucleus. POm neurons project to L1 and L5A of the primary somatosensory cortex (S1) in the rat brain. It is known that L1 modifies sensory-evoked responses through control of intracortical excitability suggesting that L1 exerts an influence on whisker responses. Therefore, thalamocortical pathways targeting L1 could modulate cortical firing. Here, using a combination of electrophysiology and pharmacology in vivo, we have sought to determine how POm influences cortical processing. In our experiments, single unit recordings performed in urethane-anesthetized rats showed that POm imposes precise control on the magnitude and duration of supra- and infragranular barrel cortex whisker responses. Our findings demonstrated that L1 inputs from POm imposed a time and intensity dependent regulation on cortical sensory processing. Moreover, we found that blocking L1 GABAergic inhibition or blocking P/Q-type Ca2+ channels in L1 prevents POm adjustment of whisker responses in the barrel cortex. Additionally, we found that POm was also controlling the sensory processing in S2 and this regulation was modulated by corticofugal activity from L5 in S1. Taken together, our data demonstrate the determinant role exerted by the POm in the adjustment of somatosensory cortical processing and in the regulation of cortical processing between S1 and S2. We propose that this adjustment could be a thalamocortical gain regulation mechanism also present in the processing of information between cortical areas.

Digital implementations of thalamocortical neuron models and its application in thalamocortical control using FPGA for Parkinson׳s disease

Due to the relay ability of sensory information and communication between cortical regions, the thalamocortical (TC) relay neuron plays an essential role in the therapy of Parkinson׳s disease. This paper first explores a series of efficient methods for the hardware implementation of TC relay neuron models, aiming to reproduce relevant biological behaviors and present appropriate feedback control in neural dynamics in thalamic systems. In addition, a modified two-dimensional TC neuron model is presented for convenient realization to decrease the complexity of the original model and promote the feasibility of the digital design, which shows significance for the large-scale network simulation of TC-based networks and the establishment of digital thalamus. A system-on-a-chip model-based control system is implemented on an FPGA using the modified TC neuron model, which is aimed at the real-time feedback control of tremor dominant Parkinsonian state. In this paper, the hardware syntheses and theoretical researches are given to illustrate the outstanding performance of the presented hardware implementation. The presented platform can be applied in both the brain-machine interface and the robotic control projects, and the proposed modular hardware framework can be extended to the real-time closed-loop treatments of other dyskinesia diseases.

The pathophysiology of Lennox-Gastaut syndrome – a review of clinico-electrophysiological studies

SUMMARYIntroduction.Lennox-Gastaut syndrome (LGS) is a type of therapy-resistant epileptic syndrome. Since the establishment of our Epilepsy Center in 1975 we have performed many studies to assess the clinical symptoms, seizure manifestations, sleep and long-term follow-up of the clinical course and changes on electroencephalographs (EEGs) in patients with LGS.Aim.To review the updated pathophysiology of LGS based on our own clinico-electrophysiological data referring to recent advances in brain research.Methods.All of our previously published and unpublished data were reviewed in order to investigate the pathophysiology of LGS and using PubMed database for relevant literature.Results and Discussion.While LGS usually occurs in infancy, it has become apparent that there is a form of late-onset LGS (L-LGS) that may occur at age eight or older. L-LGS often occurs when there is a history of encephalitis/encephalopathy or status epilepticus. The long-term progression of LGS includes mainly tonic seizures that persist and are the basis of LGS. In approximately 30% of cases, the basic symptoms of LGS remain 10 years or longer after long-term progression, while the rest lose their characteristics, although the condition is residual in 60% of cases and remission occurs in fewer than 10%. Among the characteristic seizures associated with LGS, atypical absence seizures occur in response to a diverse range of EEG features; wherein, while they are mostly short, they are accompanied by a state of enervation along with a tendency for it to be unclear when the seizure has ended. Drop attacks can in fact be categorized into those in which the subject falls over due to hypertonia in the muscles used to maintain body posture and those in which the subject falls over due to loss of tension in the posture-retaining muscles. Tonic seizures range from those manifesting in the form of extremely mild axial muscle tonicity, open eyes and respiratory changes, accompanied by high voltage, fast rhythm (averaging 14 ± 0.4 Hz), or tonicity from axorhyzomelic muscles to the peripheral muscles, accompanying global tonic seizures, and EEG features showing low voltage fast activity (averaging 22 ± 0.6 Hz) from desynchronization. A total of 1191 clinical seizures were recorded upon overnight polysomnography and videotape, and seizure symptoms and their ictal EEGs were analyzed. In LGS, seizure activity increases during slow wave sleep, inhibiting progression into the further sleep stages but falls significantly during rapid eye movement (REM) sleep.Conclusions.From the research into seizure symptoms, clinical progression, sleep and seizures during sleep, it was believed that in LGS epileptic native lesions occur due to mesencephalic reticular formation, in the thalamic reticular system and, as a result of recent of brain physiology research, it is considered that LGS is an epileptic reticulo-thalamo-cortical system disorder. This has been supported by EEG-fMRI findings (Siniatchikin et al., 2011). Further research is therefore necessary to elucidate the role of the reticular formation in controlling the thalamo-cortical networks in humans.

The hippocampus is essential for completely unconscious as well as conscious flexible memories.

This scientific commentary refers to ‘Unconscious relational encoding depends on hippocampus’ by Duss et al. (doi: 10.1093/brain/awu270). Several beliefs about the nature of organic amnesia were deeply entrenched by the early 1990s. It was believed that damage to the medial temporal lobe or its connections in the midline diencephalon and basal forebrain did not disrupt intelligence, perception, processing of information at input and immediate (short-term) memory, but selectively disrupted—following even a brief distraction—recall and recognition of recently encountered personal events or facts/concepts. In other words, amnesia was thought to affect only episodic and semantic memory, whether for pre-morbid events (retrograde amnesia) or post-morbid events (anterograde amnesia). With these kinds of memory, not only is the remembered information consciously apprehended at input and at retrieval, but the person remembering is also consciously aware that the information is a memory. That is, the person feels that the information has been encountered before, often in a particular context. In contrast, it was believed that amnesics acquired and retained other kinds of memory, such as habits and skills, normally. Although these latter types of non-declarative memory are functionally heterogeneous, they all lack the conscious feeling of memory that accompanies episodic and semantic memory. Since the late 1990s, several of these entrenched beliefs have been challenged. On the one hand, it has been argued that amnesia is not functionally unitary: while disruption of the hippocampal, fornix and anterior thalamic system impairs recall of flexible (relational) associative memories, disruption of the perirhinal cortex or its dorsomedial thalamic projection impairs inflexible item familiarity (for a review, see Montaldi and Mayes, 2010). Relational memory representations have components linked to each other as well as to other representations, which allows flexible access through multiple cues both to the representation and from it to other representations (Cohen and Eichenbaum, …

SPECTRAL CHARACTERISTICS OF BIOELECTRICAL BRAIN ACTIVITY OF STUDENTS IN LISTENING TO AUDIO-STIMULI OF DIFFERENT COMPONENT-STRUCTURAL COMPOSITION

There have been studied changes of spectral characteristics of student’s EEG in listening to audio-stimuli notable for presence of a melody and playback speed. Spectral power of theta, alpha and beta EEG-rhythms of 30 students (males and females) has been analyzed using the multifactor dispersion analysis of repeat measurements (RM MANOVA). It has been shown that high speed of playback of audio-stimuli enhanced activity of posterior associative cortex areas. Perception of the melody was characterized by a high degree of activity of the specific thalamic system and the right hemisphere neuronal structures. During perception of the melody with low playback speed in the strategy of brain processing of music, there appeared elements specific to perception of isolated rhythms.

GABAA Receptor in the Thalamic Specific Relay System Contributes to the Propofol-Induced Somatosensory Cortical Suppression in Rat

Interaction with the gamma-aminobutyric-acid-type-A (GABAA) receptors is recognized as an important component of the mechanism of propofol, a sedative-hypnotic drug commonly used as anesthetic. However the contribution of GABAA receptors to the central nervous system suppression is still not well understood, especially in the thalamocortical network. In the present study, we investigated if intracerebral injection of bicuculline (a GABAA receptor antagonist) into the thalamus ventral posteromedial nucleus (VPM, a thalamus specific relay nuclei that innervated S1 mostly) could reverse propofol-induced cortical suppression, through recording the changes of both spontaneous and somatosensory neural activities in rat’s somatosensory cortex (S1). We found that after injection of bicuculline into VPM, significant increase of neural activities were observed in all bands of local field potentials (total band, 182±6%), while the amplitude of all components in somatosensory evoked potentials were also increased (negative, 121±9% and positive, 124±6%).These data support that the potentiation of GABAA receptor-mediated synaptic inhibition in a thalamic specific relay system seems to play a crucial role in propofol-induced cortical suppression in the somatosensory cortex of rats.

2. The origin of primary bilaterally synchrony of H. Jasper, P. Gloor seen in generalized epilepsy and the secondary bilaterally synchrony of W. Blume seen in secondary generalized epilepsy

In their landmark research published in the 1950s W. Penfield and H. Jasper proposed the “centrencephalic” hypothesis proposing that “a primarily subcortical, upper brainstem and/or thalamic system with bilaterally diffuse cortical projections within which the epileptic discharge is generalized and spread 1 Gloor P. Generalized cortico-reticular epilepsies. Epilepsia 1968;9:249–62. 1 ” was the origin of primary generalized seizures with primary generalized bilaterally synchronous (PBS) discharges seen on the EEG. P. Gloor further developed on this theory and the “cortical” hypothesis of Gibbs and Gibbs and based on his clinical research of intracarotid injections of sodium amytal and metrazol in epileptic patients and the feline penicillin model proposed a “cortico-reticular” hypothesis for the above. Thus emphasizing the important role the cortex plays in PBS. W. Blume’s paper published in the Canadian Journal of Neurological Sciences (October 2, 2001), he described the concept of secondary bilateral synchrony, which he refers to a focal spike or sharp waves leading directly to “bilaterally synchronous epileptiform paroxysms.” Thus stating that the above EEG phenomenon can also been seen in be seen in patients suffering from secondary generalized seizures and may point towards a specific epileptogenic zone in the brain. This paper will aim to review the opinions of three master pioneer electro-encephalographers. The origins of primary bilateral synchrony proposed by H. Jasper and P. Gloor and the secondary bilateral synchrony (SBS) of W. Blume.

Thalamic Control of Layer 1 Circuits in Prefrontal Cortex

Knowledge of thalamocortical (TC) processing comes mainly from studying core thalamic systems that project to middle layers of primary sensory cortices. However, most thalamic relay neurons comprise a matrix of cells that are densest in the "nonspecific" thalamic nuclei and usually target layer 1 (L1) of multiple cortical areas. A longstanding hypothesis is that matrix TC systems are crucial for regulating neocortical excitability during changing behavioral states, yet we know almost nothing about the mechanisms of such regulation. It is also unclear whether synaptic and circuit mechanisms that are well established for core sensory TC systems apply to matrix TC systems. Here we describe studies of thalamic matrix influences on mouse prefrontal cortex using optogenetic and in vitro electrophysiology techniques. Channelrhodopsin-2 was expressed in midline and paralaminar (matrix) thalamic neurons, and their L1-projecting TC axons were activated optically. Contrary to conventional views, we found that matrix TC projections to L1 could transmit relatively strong, fast, high-fidelity synaptic signals. L1 TC projections preferentially drove inhibitory interneurons of L1, especially those of the late-spiking subtype, and often triggered feedforward inhibition in both L1 interneurons and pyramidal cells of L2/L3. Responses during repetitive stimulation were far more sustained for matrix than for core sensory TC pathways. Thus, matrix TC circuits appear to be specialized for robust transmission over relatively extended periods, consistent with the sort of persistent activation observed during working memory and potentially applicable to state-dependent regulation of excitability.

Functional connectivity and dynamics of cortical–thalamic networks co-cultured in a dual compartment device

Co-cultures containing dissociated cortical and thalamic cells may provide a unique model for understanding the pathophysiology in the respective neuronal sub-circuitry. In addition, developing an in vitro dissociated co-culture model offers the possibility of studying the system without influence from other neuronal sub-populations. Here we demonstrate a dual compartment system coupled to microelectrode arrays (MEAs) for co-culturing and recording spontaneous activities from neuronal sub-populations. Propagation of electrical activities between cortical and thalamic regions and their interdependence in connectivity is verified by means of a cross-correlation algorithm. We found that burst events originate in the cortical region and drive the entire cortical–thalamic network bursting behavior while mutually weak thalamic connections play a relevant role in sustaining longer burst events in cortical cells. To support these experimental findings, a neuronal network model was developed and used to investigate the interplay between network dynamics and connectivity in the cortical–thalamic system.

Advances in Therapeutic Options for Gait and Balance in Parkinson’s Disease

There is a need to explore non-dopaminergic approaches to treating balance and gait problems in Parkinson's disease (PD). There is emerging evidence on the role of cholinergic denervation of the pedunculopontine nucleus (PPN) thalamus system and falls in PD. Preliminary clinical trial data suggest that the subgroup of PD patients with frequent falls may be suitable candidates for future cholinergic augmentation clinical trials. Recent controlled clinical trials using methylphenidate have been unable to confirm earlier reports of improved gait in PD. Although progressive deterioration of axial motor symptoms occur with deep brain stimulation of the subthalamic nucleus or globus pallidus interna, new preliminary research suggests that other surgical stimulation sites, such as the PPN, may have a potential benefit on gait and balance impairments in PD. Continuing vigorous exercise and physical fitness should be highly encouraged to patients with PD who are at risk of physical deconditioning and fear of falling, but effective antifall physical therapy interventions remain an unmet clinical need.

Chemosensory learning and memory

The aim of this issue is to present an updated view of present knowledge and questions raised in the rapidly expanding field of chemosensory (taste and olfactory) learning. Taste is a powerful primary (unlearned) reinforcer, and topics such as olfactory-taste and visual taste association learning are covered in this issue. But the reinforcing properties of taste can themselves be modified, for example, by post-ingestive consequences, for example, in taste aversion learning, and this type of learning is also covered in this issue. In fact, research on the chemosensory systems has played an important role in advancing knowledge of the brain mechanisms of learning and memory. A well-known example is conditioned taste aversion (CTA). Since the time it was discovered (Garcia et al., 1955), the unique nature of CTA presented a challenge to the contemporary learning theory, and CTA contributed to present theoretical views of learning. CTA learning also became a useful tool for researchers on the neural mechanisms of learning and memory. Jan Bures was a leader in research on the brain mechanisms of CTA in Europe for several decades. We would like to dedicate this special issue to Jan Bures, who passed away on August 24, 2012, in Prague. The field of chemosensory learning is greatly saddened by the news (http://www.ctalearning.com/announcements.asp). He, together with his wife Olga Buresova, was a pioneer during the seventies in applying reversible brain inactivation techniques in order to identify the specific role of the areas forming the CTA circuits. Among other findings, he discovered the critical role of the parabrachial area in taste-visceral signal association, and the relevance of cortico-pontine connections in taste processing (Bures et al., 1998). In addition to his outstanding scientific contributions, Jan was a wonderful colleague and mentor for us and many of the contributors to the present issue and we will never forget him. The papers forming this issue are representative of the long history and great development of the field thanks to the use of different species and a variety of technical and theoretical approaches. The widely ranging review by Yamamoto and Ueji (2011) of flavor learning including both learned food preferences and aversions, and the paper by Scott (2011) reviewing classic knowledge on the brain mechanisms of CTA, highlight the advances in the field during the last decades. Wider and more complex brain systems than previously thought contribute to flavor learning, with age-dependent interactions between areas such as the insular cortex, amygdala, hippocampal, thalamic, and reward systems (Gamiz and Gallo, 2011). The evidence reported by Neseliler et al. (2011) using an in vivo genetically modified rodent model of hypercholinergic innervation is an example of the value of new approaches to support the hypothesis linking acetylcholine and CTA. As Guzman-Ramos and Bermudez-Rattoni (2011) describe, major research advances have been made on the cascade of molecular changes involved in the consolidation of CTA taking place during the post-acquisition period. Remarkable progress has also been made in the field of food preferences. de Araujo (2011) provides a review that includes data obtained both in rodents and Drosophila on the role of taste and energy-sensing systems receiving gastrointestinal and post-absorptive signals in the formation of long-lasting preferences mediated by dopamine release. The elegant experimental work using a variety of techniques reported by Oliveira-Maia et al. (2012) adds evidence on this topic demonstrating the role of the insular cortex in detecting the postingestive effects of sucrose intake. Closely linked to taste learning in detecting chemical molecules is olfactory learning. As Sandoz (2011) shows in his review, the honeybee has been a model for applying behavioral, neurophysiological and neuroanatomical techniques to research on olfactory learning. Two separate models of the role in olfactory learning of the rat olfactory bulb (Auffarth et al., 2011) and the human glomerulus (Schaefer and Margrie, 2012) are presented. Finally, Rolls (2011) reviews evidence from primates including humans on the value of taste as a primary reinforcer and the role of the orbitofrontal cortex in building olfactory-taste, and visual-taste associations. He also shows how top–down cognition and attention influence taste and olfactory processing in ways that must involve learning, and also considers the cortical mechanisms involved in taking decisions about olfactory and taste stimuli.

Quantitative Characterization of Primary Structural Modules in the Relay Nuclei of the Sensory Systems of the Human Thalamus

The modular organization of neurons in the ventral posterior medial (VPM) and ventral posterior lateral (VPL) relay nuclei of the thalamic sensory systems in adult humans was studied. Specimens obtained from six subjects aged 48–70 years were fixed in 4% paraformaldehyde and sections of thickness 40 μm were cut and stained by the Kluver–Barrera method. The numbers of neurons in group and chain modules were determined, along with the field profile areas (FPA) of neuron bodies forming modules, the total numbers of satellite glial cells, and the numbers of identified glial cells (oligodendrocytes and astrocytes) in modules. The FPA of neuron bodies were measured using a digitizer on accurate drawings of cells made with a drawing device (magnification ×1025). Data were entered into a computer and analyzed using a nonparametric analysis program. Neurons in group and chain modules were of intermediate size, from 201 to 350 μm2, in each nucleus. Most group and chain modules in the VPM and VPL nuclei of the human thalamus consisted of 3–4 cells. There were 8.4 satellite gliocytes per group module in the VPM, compared with 8.6 in chain modules; in the VPL, group modules contained 7.7 gliocytes and chain modules contained 8.2 gliocytes. The numbers of oligodendrocytes in VPM and VPL modules were three times greater than the numbers of astrocytes.

Projections from cingulate cortex to the cat’s thalamic reticular nucleus

The cingulate cortex (CG) and the adjacent region designated as the splenial visual area (SVA) project to areas of the extrageniculate thalamic system that are concerned with processing visual information. En route to the thalamus, they pass through the thalamic reticular nucleus (TRN), an important source of thalamic inhibition. We wished to determine whether SVA axon collaterals projected to the previously defined visual sector of the TRN or a separate projection zone and did this differ from the projection zone of CG. We iontophoretically injected different neuroanatomical tracers into several locations within CG/SVA and traced the labeled axons through the TRN. The CG and SVA have a projection zone that only partially overlaps the dorsorostral regions of the visuocortical projection zone; there was no evidence to suggest separate SVA and CG zones or tiers of label within the TRN. The projection formed only a weak topographic map in the TRN, which is largely defined in the rostrocaudal axis and is similar to that of the area 7 projection; both projections have a high degree of overlap in the dorsal TRN. We postulate that CG/SVA may be involved in the initiation of orientation behaviors via stimulation of thalamic nuclei and attentional mechanisms of the TRN.