PubMed Health⌕ Search

Biomedical subjects

V Bracha

Publications and source records attributed to V Bracha.

27 records · Page 2Linked to original sources
PubMed1995

Relationship of simultaneously recorded cerebellar nuclear neuron discharge to the acquisition of a complex, operantly conditioned forelimb movement in cats.

This study was designed to examine the changes in the modulation of small populations of cerebellar neurons during the acquisition of a complex, operantly conditioned forelimb task in cats. The experiments are based on the general postulate that, during the learning of a complex motor behavior, the cerebellum is important for generating a coordinated movement that meets the task's objectives, and that, as the cerebellum participates in this process, it acts to reinforce the effective motor pattern once it has been established. This specific study examines whether the changes in the modulation of cerebellar nuclear neurons during the learning of this task are consistent with this view. Cats were required to learn to move the manipulandum through a novel pattern of 2-3 consecutive straight grooves connected end to end in different spatial configurations, e.g., the letter L, an inverted L, and the letter C. Throughout the acquisition process, 6-12 single units were recorded simultaneously in the cerebellar nuclei, and the kinematics of the movement were evaluated using an Optotrak system. Cells were recorded from the two interposed nuclei and the dentate nucleus in these initial studies. Trials were sorted off-line based on the level of skill at which the required movement was performed. This was assessed using several objective criteria such as movement times, kinematic characteristics, and smoothness (number of peaks in the velocity profile). Event-related histograms then were constructed from each group of sorted trials. Changes in modulation related to a specific event were measured in successive histograms for each neuron.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

On the cerebellum, cutaneomuscular reflexes, movement control and the elusive engrams of memory.

This review focuses on the role of the cerebellum in regulating cutaneomuscular reflexes and provides a hypothesis regarding the way in which this action contributes to the coordination of goal-directed movements of the extremities. Specific attention is directed towards the cerebellum's role in conditioned and unconditioned eyeblink reflexes and limb withdrawal reflexes as models of its interactions with the cutaneomuscular reflex systems. The implications regarding the cerebellum as a storage site for motor engrams also is discussed in the context of these two behaviors. The proposed hypothesis suggests that the cerebellum regulates important features of the cutaneomuscular reflex circuits including the integration of their activity with descending pathways in a manner that implements these fundamental reflex circuits in the organization and control of goal-directed movements of the extremities.

Animals↗
PubMed1994

Effects of muscimol inactivation of the cerebellar interposed-dentate nuclear complex on the performance of the nictitating membrane response in the rabbit.

Intracranial microinjections of the GABAA agonist muscimol were used to assess the involvement of the dentato-interposed cerebellar nuclear complex in the performance of the conditioned (CR) and unconditioned (UR) nictitating membrane responses in the rabbit. Specifically, the experiments test the hypothesis that the cerebellar nuclei are involved in the performance of both the CRs and URs. The experiments employed temporary nuclear lesions to disrupt the CRs in order to examine parallel effects on URs. Animals were conditioned in a standard delay conditioning paradigm. Injection sites at which the muscimol application disrupted execution of the CRs were identified in each rabbit. Once these sites were found, the effects of muscimol and saline injections were evaluated while alternating paired trials with unpaired trials in which only the unconditioned stimuli were applied. There are two main findings in the present study. First, the activation of the GABAA receptors in the dentato-interposed cerebellar nuclear region reduced the amplitude and increased the latency of the UR. This change in the UR closely paralleled the disruption of the CR. This observation is consistent with the notion that the cerebellum is involved in the regulation of defensive flexion reflexes. Second, cerebellar nuclear inactivation did not eliminate the tone-induced enhancement of the UR. This finding suggests the presence of cerebellum-independent circuits subserving the intermodal interaction between the conditioned and unconditioned stimuli.

Animals↗
PubMed1993

The temporary inactivation of the red nucleus affects performance of both conditioned and unconditioned nictitating membrane responses in the rabbit.

These experiments are part of a series of studies examining the role of the red nucleus in the performance of the conditioned and unconditioned nictitating membrane reflexes in the rabbit. Specifically, the experiments test the hypothesis that the temporary inactivation of the red nucleus selectively affects the performance of the conditioned reflex. The experiments were designed to assess the effects of lidocaine and control saline microinjections on conditioned as well as unconditioned responses in both paired and unpaired trials. Rabbits were chronically implanted with cannulae through which small injecting tubes were passed stereotaxically to the red nucleus. The animals were conditioned using a delay paradigm in which a 1 kHz tone and an air puff applied to the cornea were used as the unconditioned and conditioned stimulus, respectively. Once conditioned, the effects of either lidocaine or saline injection were evaluated while alternating paired trials with unpaired trials in which only the air puff was applied. The principal finding of this study was that the amplitudes of both the conditioned and unconditioned responses were reduced following lidocaine injection into the red nucleus. The effect on the unconditioned response amplitude could not be ascribed to any interaction between the conditioned and unconditioned responses, since it also was present in the unpaired trials. The reduction in amplitude of the conditioned and unconditioned responses was shown to be correlated with changes in other characteristics of the same responses. The data suggest that the red nucleus contributes to the performance of both the conditioned and unconditioned nictitating membrane reflexes and consequently is not likely to be involved only in pathways responsible for mediating and/or storing the engram for the conditioned reflex.

Acoustic Stimulation↗
PubMed1993

Real time operations of the cerebellar cortex.

This manuscript reviews a series of experiments which support the notion that the cerebellum and more specifically the cerebellar cortex is principally involved in real time operations required for the regulation of coordinated motor activity. Experiments are reviewed which illustrate: (1) that the climbing fiber inputs to Purkinje cells can induce a short-lasting enhancement of their responses to mossy fiber-granule cell-parallel fiber inputs, (2) that the cerebellum is not essential for the acquisition and performance of the classically conditioned nictitating membrane reflex (NMR) of the rabbit, and (3) that the observations resulting from the microinjection of lidocaine and multiple single unit recordings within the brainstem support the notion that cell populations in this region may participate in establishing the modifications in neuronal interactions required for the acquisition of the conditioned NMR. In addition, preliminary data are shown comparing the capacity of a normal subject and a patient with a massive ipsilateral cerebellar stroke to learn certain tracing tasks and to redraw these learned tracing movements 90 degrees to the orientation of the original image. The data support the notion that the cerebellum is essential, not for the initial learning of the tracing movement, but rather for performing the learned movement with the required rotation of the original image.

Animals↗
PubMed1992

Distribution of c-fos expression in brainstem neurons associated with conditioning and pseudo-conditioning of the rabbit nictitating membrane reflex.

Experiments were performed to test the hypothesis that there is a characteristic distribution of neuronal c-fos expression associated with the classical conditioning of the rabbit nictitating membrane reflex (NMR). Rabbits were divided into two groups: a conditioning group that received paired tone and airpuff stimuli in a traditional delay NMR conditioning paradigm and a pseudo-conditioning group in which the same number of tone and airpuff stimuli were applied but without being paired. Labeling was present in similar brainstem nuclei in both groups of animals. The labeled sites included trigeminal and auditory nuclei in the classical pathway for the nictitating membrane reflex as well as other nuclei such as the raphe nuclei and those in the ventrolateral medulla (VLM). However, there were quantitative differences in the labeling between the two groups. There were significantly more labeled nuclear profiles in the trigeminal nucleus of the pseudoconditioned rabbits, but more labeled nuclear profiles in the raphe nuclei in the conditioned animals. Interestingly, the ratio of the labeling in the raphe versus the VLM strongly differed between the two groups.

Animals↗
PubMed1991

Selective involvement of the spinal trigeminal nucleus in the conditioned nictitating membrane reflex of the rabbit.

These experiments were performed to test the hypothesis that a region associated with the trigeminal nuclear complex is selectively involved in mediating the classically conditioned nictitating membrane reflex in the rabbit. Microinjections of Lidocaine were used to produce a temporary, localized block of neural activity following the conditioning of the reflex using a standard tone/air puff-paired stimulus paradigm. Data indicate that the injection of Lidocaine at the medial pars oralis/reticular formation junction results in a selective suppression of the conditioned reflex.

Animals↗
PubMedDate not supplied

Impaired capacity of cerebellar patients to perceive and learn two-dimensional shapes based on kinesthetic cues.

This study addresses the issue of the role of the cerebellum in the processing of sensory information by determining the capability of cerebellar patients to acquire and use kinesthetic cues received via the active or passive tracing of an irregular shape while blindfolded. Patients with cerebellar lesions and age-matched healthy controls were tested on four tasks: (1) learning to discriminate a reference shape from three others through the repeated tracing of the reference template; (2) reproducing the reference shape from memory by drawing blindfolded; (3) performing the same task with vision; and (4) visually recognizing the reference shape. The cues used to acquire and then to recognize the reference shape were generated under four conditions: (1) "active kinesthesia," in which cues were acquired by the blindfolded subject while actively tracing a reference template; (2) "passive kinesthesia," in which the tracing was performed while the hand was guided passively through the template; (3) "sequential vision," in which the shape was visualized by the serial exposure of small segments of its outline; and (4) "full vision," in which the entire shape was visualized. The sequential vision condition was employed to emulate the sequential way in which kinesthetic information is acquired while tracing the reference shape. The results demonstrate a substantial impairment of cerebellar patients in their capability to perceive two-dimensional irregular shapes based only on kinesthetic cues. There also is evidence that this deficit in part relates to a reduced capacity to integrate temporal sequences of sensory cues into a complete image useful for shape discrimination tasks or for reproducing the shape through drawing. Consequently, the cerebellum has an important role in this type of sensory information processing even when it is not directly associated with the execution of movements.

Adult↗