Changes in the impulse activity of neurons of the human thalamic ventrolateral nucleus during voluntary movement

Functional differences were revealed in evoked activity of two types (A and B) of units of the human thalamic ventro-lateral nucleus (VL). Collective activities of these polyfunctional neurons were selectively related to triggering and execution phases of movement. Common character of dynamics of the responses seems to be due to similar polyfunctional nature as well as to the functional role of these two complementary elements in the motor signal transmission. The collective activities reflect in the VL the integrative processes related to processing and programming of generalised parameters of motor signals, but unrelated to performance of a concrete motor act.     

Reversible lesions of the red nucleus during acquisition and retention of a classically conditioned behavior in rabbits.

Previous lesion, recording, and stimulation studies implicated the cerebellum and its associated brain-stem circuitry as essentially involved in classical conditioning of discrete, somatic muscle responses. A prior study of interpositus cooling showed that the formation of memory was prevented. The present study assesses the red nucleus (RN) for its role in the plasticity associated with learning and memory by using local cooling as a reversible lesion technique. A cooling probe was implanted lateral to the RN. Recording electrodes were implanted in the right RN and the left interpositus nucleus (IPN). Animals were trained for 6 days with the cooling probe activated. No behavioral CRs developed, and multiple unit recordings related to learning did not develop in the RN. However, a learning related model did develop in the IPN. After 5 days of training while cooling, animals were given 5 days of normal training (cooling probe inactive) to assess retention. Substantial savings were evident when normal training was given. CRs appeared quickly on the 1st day of normal training, and multiple unit models were present in both RN and IPN. Results support the idea that the red nucleus is a necessary efferent for the memory trace formed in the cerebellum. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reversible lesions of the cerebellar interpositus nucleus during acquisition and retention of a classically conditioned behavior.

Previous lesion, recording, and stimulation studies have implicated the cerebellum and its associated circuitry as essentially involved in classical conditioning of discrete, somatic muscle responses. In 2 experiments, the interpositus nucleus of the cerebellum as assessed for the plasticity associated with learning and memory of the nictitating membrane (NM) response by using local cooling as a reversible lesion technique. In well-trained animals (Exp 1), NM conditioned responses (CRs) were abolished during cooling of the interpositus but reappeared when the interpositus returned to body temperature. This cooling–warming protocol could be repeated many times. Cooling could be prolonged (1 session, ～1 hr) with recovery of NM CRs as tested on the next day. Multiple-unit recordings related to learning were also absent in the interpositus and red nucleus during cooling. In naive animals (Exp 2), both behavioral and unit CRs did not develop while training with cooling. There was no evidence of savings when training continued without cooling: Behavioral and unit CRs developed as if the animals were still naive. These results support the idea that the interpositus nucleus of the cerebellum is the critical locus for learning and memory of this classical CR. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of pairing red nucleus and motor thalamic lesions on reaching toward moving targets in cats.

The small effects of bilateral lesions of motor thalamus on motor control and the transient deficits induced by bilateral kainic red nucleus (RN) lesions have been explained by a parallel competitive role of the cortico- and rubro-spinal pathways: Either pathway can take over motor control if the other is damaged. In this study the effect of bilateral and simultaneous lesions of both RN and motor thalamus was analyzed on cats overtrained to reach toward a moving target. After lesion, accuracy was impaired, movement onset was delayed, and movement execution was perturbed. However, postoperative retraining led to full recovery of the preoperative accuracy level although movement latency remained higher. The relative mildness of the long-lasting deficit after lesioning 2 main motor brain structures underlines the robustness of overlearned movements and widens the idea of parallelism in the motor system to other (subcortical?) pathways. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Human thalamic nucleus mediating taste and multiple other sensations related to ingestive behavior

Until now, taste was the only primary sensory modality for which the human central nervous system pathways were unknown. We report sensations evoked by stimulation at microampere current levels in the region of the human thalamic nucleus (ventralis caudalis parvocellularis internis) corresponding to the monkey taste relay nucleus. Stimulation in this region during awake neurosurgical procedures evoked special visceral/somatic (taste/pungent smell), general visceral (fullness of a hollow viscus), as well as painful and nonpainful general somatic sensations. General somatic or visceral sensation was evoked by stimulation at 80% of sites where special visceral/somatic sensation was evoked. These results suggest that primate taste relay mediates multiple sensations in addition to taste.     

Comparative anatomical study of ventrolateral thalamic mass in humans and monkeys

Cytoarchitecture and enzyme activity in the ventrolateral thalamic mass of humans and monkeys were examined using conventional Nissl, myelin stain and histochemical methods. According to the data obtained from cytometric analysis, the histogram patterns of cell dimensions and cell density in each ventrolateral thalamic nucleus in humans and monkeys were very similar. Moreover, acetylcholinesterase-stained sections revealed a parcellation of the ventrolateral thalamic nuclei that could be correlated with that in the monkey thalamus. Apart from differences of size, the nuclei of the human and monkey thalamus are remarkably similar. We proposed accordingly that a new parcellation of human thalamic nuclei be based on cytometric analysis and histochemical staining.     

Motion integration in a thalamic visual nucleus

Thalamic nuclei have long been regarded as passive relay stations for sensory information en route to higher level processing in the cerebral cortex. Recently, physiological and theoretical studies have reassessed the role of the thalamus and it has been proposed that thalamic nuclei may actively participate with cortical areas in processing specific information. In support of this idea, we now show that a subset of neurons in an extrageniculate visual nucleus, the lateral-posterior pulvinar complex, can signal the true direction of motion of a plaid pattern, indicating that thalamic cells can integrate different motion signals into a coherent moving percept. This is the first time that these computations have been found to occur outside the higher-order cortical areas. Our findings implicate extrageniculate cortico-thalamo-cortical loops in the dynamic processing of image motion, and, more generally, as basic computational modules involved in analysing specific features of complex visual scenes.     

Projections from the lateral mammillary nucleus to the anterodorsal thalamic nucleus in the rat

There has been an abundance of research on the connections of the mammillary bodies but the projections from the lateral mammillary nucleus to the anterodorsal thalamic nucleus has remained a gray area due to a dearth of material which directly addresses the details of this pathway. This study seeks to further define the nature of this particular nerve connection within the mammillothalmic tract. The technique employed is fluorescent nerve tract tracing using two fluorescent tracers implanted separately into each anterodorsal thalamic nucleus then followed retrogradely to the soma of the neurons in the lateral mammillary nucleus. Fluorescent photomicrography allowed us to document the single and double labeled cells of the lateral mammillary nucleus. The single labeled cells can be categorized into ipsilaterally projecting neurons and contralaterally projecting neurons. About half of all labeled cells were bilaterally projecting double-labeled, a third was ipsilaterally projecting single-labeled and the remainder were contralaterally projecting single labeled-cells. There were no labeled cells traced to the medial mamillary nucleus. The mammillary bodies play an important role in the limbic circuitry and a part of the so-called "Papez Circuit". The pathway by which the mammillary body projects to the other structures of the limbic system and the way it connects the limbic system to other parts of the brain like the tegmentum is not fully understood. This clarification of the connection between the lateral mammilary nucleus and the anterodorsal thalamic nucleus is but one of the contemplated pathways.     

Effect of electrical stimulation of the thalamic Vim nucleus on hand tremor during stereotactic thalamotomy

OBJECTIVE: The aim of this study was to analyze the correlation between neuronal responses in the thalamic ventralis intermedius (Vim) nucleus to peripheral, natural stimulation and the modulation of tremor by electrical stimulation during stereotactic thalamotomy. DESIGN AND METHODS: The authors studied 36 patients with hand tremor using a microelectrode. The responses of tremor to electrical stimulation were analysed electromyographically. Sixty stimulation sites were divided into three groups. RESULTS: Group A (20 sites) where responses to stretching of the contralateral forearm muscles were recorded. Group B (26 sites) where responses to stretching of the other muscles of the upper extremity were recorded. Electrical stimulation at sites in groups A and B temporarily suppressed the contralateral tremor, but the minimum current intensity to suppress tremor at sites in group A was less than that in group B. Electrical stimulation in group C (14 sites), where kinesthetic responses of contralateral lower extremity were recorded, resulted in increased amplitude of hand tremor. Selective coagulation including the area of tremor suppression resulted in abolition of the tremor in all patients. CONCLUSIONS: These results suggest that the most effective site for thalamotomy may also be suitable for chronic stimulation in the Vim nucleus.     

Lesions of the amygdala central nucleus abolish lipoprivic-enhanced responding during oil-predicting conditioned stimuli.

T. L. Davidson, A. M. Altizer, S. C. Benoit, E. K. Walls, and T. L. Powley (see record 1997-43076-013) reported that rats show facilitated responding to conditioned stimuli (CSs) that predict oil, after administration of the lipoprivic agent, Na-2-mercaptoacetate (MA). This facilitation was blocked by vagal deafferentation. The present article extends that investigation to another structure, the amygdala central nucleus (CN). The CN receives inputs from dorsal vagal nuclei, and neurotoxic lesions of this nucleus are reported to abolish feeding in response to lipoprivic challenges. In Experiment 1, rats with ibotenic acid (IBO) lesions of the CN failed to show enhanced appetitive responding during oil-predicting CSs after administration of MA. Experiment 2 used a conditioned taste-aversion procedure to establish that rats with IBO lesions of the CN were able to discriminate the tastes of sucrose and peanut oil and had intact CS–US representations. It is concluded that the amygdala CN is a necessary structure for the detection of lipoprivic challenges. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Extracellular amino acid levels in the interpositus nucleus during classical eyeblink conditioning in alert cats.

The extracellular levels of selected amino acids in the cerebellar posterior interpositus nucleus (PIN) during classical eyeblink conditioning was analyzed in alert cats using a delay paradigm. Animals were prepared for the chronic recording of eyelid movements (with the magnetic search-coil technique) and the electromyographic activity of the orbicularis oculi muscle. With the help of a guide and push-pull cannulae, selected PIN sites were perfused daily during classical eyeblink conditioning. The perfusate was sampled at intervals of 5 min and analyzed with a high-pressure liquid chromatography- electrochemical detection (HPLC-EC) method. The analysis of push-pull perfusate revealed a significant increase in the release of glycine, taurine, and glutamate across the successive conditioning sessions, in parallel with the acquisition of eyelid conditioned responses (CRs). Both CRs and extracellular levels of these three amino acids returned to control values during extinction. Other amino acids (alanine, GABA, glutamine, serine, and threonine) did not undergo modifications in their extracellular concentrations across the training. Results are discussed with regard to the role of PIN in this type of associative learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of electrical stimulation of the hippocampus on the behavior of cats and their defensive conditioned responses in a shuttle-box

In seven cats the effect of posterior hippocampal stimulation on the number of passings over a transverse bar in a shuttle-box was determined before and after induction of a conditioned avoidance reaction in the same experimental situation. The effect of hippocampal stimulation on the reaction was also studied applying it during the conditioning stimulus. It was observed in these experiments that a behavior imitating the conditioned reaction acquired during training, appeared in most cases during stimulation. It was also found that only strong stimulation of the posterior hippocampus applied together with the conditioning stimulus inhibited the reaction.     

The roles of thalamic nucleus submedius in nociception and pain modulation

Recent studies on the roles of thalamic nucleus submedius (Sm) in nociception and pain modulation were reviewed in this article in combination with own our works. Results of these studies showed that Sm may be involved in effective-motivational aspects of pain, and that Sm-VLO-PAG may constitute a pathway of nociceptive modulation which may depress the nociceptive inputs at the spinal cord level via the brain-stem descending inhibitory system, thereby mediate a negative feedback regulation of pain.     

Morphology of rats AV thalamic nucleus in light and electron microscopy

The structure of the rat's antero-ventral thalamic (AVTh) nucleus has been investigated in order to provide background information for the accompanying study in which an attempt was made to identify the synaptic terminals of the different afferent fiber systems to this nucleus by means of both EM autoradiography and the EM degeneration techniques. Nissl stained sections showed that the rat's AVTh nucleus contains mainly relatively light staining neurons which in Golgi material were found to possess tufted dendrites. In EM material three types of synaptic terminals were found which showed a topical distribution over the neuronal surface. Soma and stem dendrites carry a limited number of terminal with symmetrical synapses and flattened vesiclesmproximal dendrites carry mainly large asymmetrical synaptic terminals while distal dendrites are crowded with small asymmetrical synaptic terminals.     

Emergent spindle oscillations and intermittent burst firing in a thalamic model: specific neuronal mechanisms

The rhythmogenesis of 10-Hz sleep spindles is studied in a large-scale thalamic network model with two cell populations: the excitatory thalamocortical (TC) relay neurons and the inhibitory nucleus reticularis thalami (RE) neurons. Spindle-like bursting oscillations emerge naturally from reciprocal interactions between TC and RE neurons. We find that the network oscillations can be synchronized coherently, even though the RE-TC connections are random and sparse, and even though individual neurons fire rebound bursts intermittently in time. When the fast gamma-aminobutyrate type A synaptic inhibition is blocked, synchronous slow oscillations resembling absence seizures are observed. Near-maximal network synchrony is established with even modest convergence in the RE-to-TC projection (as few as 5-10 RE inputs per TC cell suffice). The hyperpolarization-activated cation current (Ih) is found to provide a cellular basis for the intermittency of rebound bursting that is commonly observed in TC neurons during spindles. Such synchronous oscillations with intermittency can be maintained only with a significant degree of convergence for the TC-to-RE projection.     

GABAergic and pallidal terminals in the thalamic reticular nucleus of squirrel monkeys

The ultrastructure of synaptic terminals from the external segment of the globus pallidus and of other synaptic terminals positive for gamma-aminobutyric acid (GABA) was examined in the thalamic reticular nucleus (TRN) of squirrel monkeys. Two GABA-positive terminals types were commonly encountered within the TRN neuropil. The most common type of GABAergic terminals (F terminals) are filled with dispersed pleomorphic synaptic vesicles and clusters of mitochondria. These terminals establish multiple symmetric synapses upon the somata and dendrites of TRN neurons. The external pallidal terminals, labeled with WGA-HRP, arise from thinly myelinated axons and correspond to the medium to large F terminals. A less prevalent population of smaller GABAergic synaptic profiles was also identified. The synaptic profiles in this second group contain considerably fewer pleomorphic synaptic vesicles in small irregular clusters and fewer mitochondria, establish symmetric synapses, are postsynaptic to other axonal terminals, are presynaptic to dendrites and soma, and are unlabeled following pallidal injections of WGA-HRP.     

Contrasting expressions of aggressive behavior released by lesions of the central nucleus of the amygdala during wakefulness and rapid eye movement sleep without atonia in cats.

Whether damage to the central nucleus of the amygdala (Ace) contributes to the predatory-like attack sometimes observed in rapid eye movement sleep without atonia (REM-A), created in cats by bilateral pontine lesions, was examined. Such lesions eliminate REM sleep skeletal muscle atonia and release elaborate behavior. Unilateral damage to the Ace alone increased affective defensive aggressive behavior toward humans and conspecifics without altering predatory behavior in wakefulness. Pontine lesions added at loci normally not leading to aggression induced predatory-like attacks in REM-A as well as the waking affective defense. Alterations of autonomic activity, the absence of relevant environmental stimuli in REM-A, or both may explain the state-related differences. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Transient features of the thalamic reticular nucleus in the human foetal brain

The architectonic organization and neuronal types of the human foetal reticular nucleus (RN)--with special reference to transient characteristics--have been investigated using antisera against calretinin, parvalbumin and neurofilament epitopes of somata and dendrites (SMI 311). The RN consists of four subdivisions (clearly distinguishable in the 6/7th gestational month): The main portion appears as a prominent structure on account of its extension and high packing density of neurons which coexpress calretinin and parvalbumin. These two calcium-binding proteins are also expressed by the perireticular nucleus forming a conspicuous grey within the internal capsule. Perireticular cells form clusters which are in continuity with the main portion, globus pallidus, ganglionic eminence and pregeniculate nucleus. In double-labellings, a medial subnucleus stands out distinctly as it only expresses calretinin. SMI 311-immunopreparations show neurons revealing a high degree of diversification and elaborated dendritic trees. Several transient characteristics become obvious: the perireticular nucleus, not visible in the adult, represents a distinct entity in the human foetal brain. The main portion and the pregeniculate nucleus appearing as prominent greys are dramatically reduced in size later on. The percentage of RN-neurons expressing calretinin, the diversity of neuronal types and elaborated dendritic trees are reduced. The transient features can be correlated with the RN's putative functional roles in development: early RN-afferents to the dorsal thalamus may represent pioneer fibres providing guiding cues for outgrowing axons from or into the thalamus. Moreover, the RN may serve as an intermediate target for growing axons which are sorted and directed towards different final targets.