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A R Gibson

Publications and source records attributed to A R Gibson.

At least 19 recordsLinked to original sources
PubMed1998

Organization of ascending pathways to the forelimb area of the dorsal accessory olive in the cat.

The purpose of these experiments was to define the topography of cuneate and spinal projections to the forelimb representation in the rostral dorsal accessory olive (rDAO). We were interested in determining whether the spinal and cuneate inputs constitute a homogeneous afferent source, and whether there is evidence that they serve different functional roles. We were also interested in determining whether the somatotopy of rDAO is the result of a point-to-point projection from its afferent sources, or whether the projection suggests a reorganization of afferents at the olive. Single unit recording was used to identify specific regions of rDAO, and the topography of inputs to the identified regions was determined by using wheat germ agglutinin-horseradish peroxidase (WGA-HRP) as a tracer. The results from retrograde tracing were confirmed by using WGA-HRP as an anterograde tracer from input sources. The cuneate and spinal neurons providing input to rDAO constitute two distinct neural populations. One consists of cells in the caudal cuneate nucleus and lamina VI of the rostral two cervical segments, the other consists of cells in the rostral cuneate nucleus. The cells in the caudal cuneate nucleus and the rostral cervical segments are large, multipolar neurons that form a single column of rDAO input cells. The column of cells projects to the contralateral rDAO in a topographic fashion with rostral regions of the column projecting to rostral rDAO, which contains cells that respond to somatosensory stimulation of the contralateral shoulder, trunk, and proximal forelimb. Caudal regions of the column project to caudal rDAO, which contains cells that respond to stimulation of the distal forelimb. Despite this topography, there is a large degree of overlap in the terminations from neighboring regions of the input column, indicating that a major reorganization occurs at the rDAO. The projection from the rostral cuneate nucleus arises from small neurons that project bilaterally to rDAO, and the input from the rostral cuneate nucleus lacks a clear topography. We propose that input from the cell column is responsible for the somatosensory sensitivity of rDAO neurons, whereas input from rostral cuneate is most likely modulatory, probably inhibitory, in nature.

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PubMed1998

Construction of a reach-to-grasp.

Reaching out to grasp an object requires the coordinated action of many different areas of the brain. Each area probably makes a unique contribution to the control of limb movement. We have studied the discharge of interpositus, the output nucleus of intermediate cerebellum, and magnocellular red nucleus, which connects interpositus to the spinal cord. The neurons in these areas discharge at high rates only if a hand movement is included with the reach, and discharge pattern is similar regardless of reach direction. Therefore, interpositus and magnocellular red nucleus are involved primarily in grasp control during the reach-to-grasp; other areas must be controlling the reach. Several other areas of the brain, including the reticular formation, rostral mesencephalon, superior colliculus and motor cortex, are active during reaching. The output from these descending systems converges on interneurons at spinal level C1 and C2 which, in turn, project to level C6, where motor neurons innervating shoulder muscles are located. We hypothesize that reach control is achieved by the convergence of multiple descending pathways onto a complex spinal interneuronal system.

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PubMed1998

Red nucleus stimulation inhibits within the inferior olive.

Red nucleus stimulation inhibits within the inferior olive. J. Neurophysiol. 80: 3127-3136, 1998. In the anesthetized cat, electrical stimulation of the magnocellular red nucleus (RNm) inhibits responses of rostral dorsal accessory olive (rDAO) neurons to cutaneous stimulation. We tested the hypothesis that RNm-mediated inhibition occurs within the inferior olive by using stimulation of the ventral funiculus (VF) of the spinal cord in place of cutaneous stimulation of the hindlimb. Fibers in the VF terminate on hindlimb rDAO neurons, so inhibition of this input would have to occur within the olive. rDAO responses elicited by VF stimulation were inhibited by prior stimulation of the RNm, indicating that inhibition occurs within the olive. In contrast, evoked potentials recorded from the VF or dorsal columns following hindlimb stimulation were not affected by prior stimulation of RNm, indicating that stimulation of the RNm does not inhibit olivary afferents at spinal levels. RNm stimulation that inhibited rDAO responses had little effect on evoked somatosensory responses in thalamus, indicating that inhibition generated by activity in RNm may be specific to rDAO. To test limb specificity of RNm-mediated inhibition, conditioning stimulation was applied to the dorsolateral funiculus at thoracic levels, which selectively activates RNm neurons projecting to the lumbar cord. Stimulation at thoracic levels inhibited evoked responses from hindlimb but not forelimb regions of rDAO, suggesting that inhibitory effects of RNm activity are limb specific. Several studies have reported that olivary neurons have reduced sensitivity to peripheral stimulation during movement; it is likely that RNm-mediated inhibition occurring within the olive contributes to this reduction of sensitivity. Inhibition of rDAO responses by descending motor pathways appears to be a salient feature of olivary function.

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PubMed1996

NIH rating system.

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National Institutes of Health (U.S.)↗
PubMed1996

Reduction of rostral dorsal accessory olive responses during reaching.

1. Rostral dorsal accessory olive (rDAO) neurons are sensitive to light touch but have little or no discharge during active movement. We hypothesize that sensitivity of the rDAO is reduced during movement. To test this hypothesis, we evaluated sensitivity of rDAO neurons as cats reached out and retrieved a handle. On selected trials, mechanical or electrical perturbations to the forelimb were presented, and responses of rDAO neurons to the disturbances were recorded. 2. All rDAO units were highly sensitive to somatosensory stimuli during periods of stance. The cells responded to stimuli such as touch to hairs or light taps to the platform on which the cat was standing. 3. Discharges of rDAO neurons showed little or no synchronization to any aspect of the reaching task. rDAO neurons failed to fire to mechanical perturbations of the food handle during retrieval or hold phases of the task, even when their receptive fields included the surface of the paw in contact with the handle. 4. Electrical stimulation of the skin produced the greatest evoked response at all rDAO recording sites when the cats were at stance. Stimulation at any time during the reaching task, including periods of holding and licking, produced lower-amplitude evoked responses. The reduction in evoked response could be large and was restricted to the limb performing the task. 5. The data support the hypothesis that the cutaneous sensitivity of the rDAO is reduced during behavior. However, the inhibition does not appear to be tailored to specific times during the task or to neurons with specific receptive field locations on the actively moving limb. The reduction in sensitivity is as likely to be dependent on limb posture as on movement. We conclude that the rDAO discharge provides the cerebellum with information about vibration or contact during stance; it does not provide reliable information about undisturbed or disturbed movement. Climbing fiber input from rDAO might be useful in the preparation to make a movement, but it is probably not useful for correction of movement errors.

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PubMed1996

Activity of interpositus neurons during a visually guided reach.

Neurons in the cerebellar interpositus nucleus greatly increase their discharge rates when a monkey reaches out to grasp an object. However, when the monkey is required to track a target on a screen by moving a manipulandum, the increase in discharge rate is relatively small or nonexistent. Moving the hand directly to a target is a visuomotor task that may be fundamentally different from a remote tracking task. We hypothesize that the interpositus nucleus is specialized for direct visual guidance of the limb or, alternatively, interpositus is specialized for controlling hand movements required to grasp an object. A monkey was trained to hold a sensor and move it directly over a visual target to obtain water reward. Small drawers were mounted next to two of the targets; on some trials a drawer would open so that the monkey would reach out and retrieve a raisin that had been placed in it. Interpositus neurons discharged strongly during reach to grasp the raisin but not when the monkey was positioning the sensor over the target. For individual cells, discharge pattern and amplitude were largely independent of the size and direction of the reach to grasp, suggesting that interpositus does not control direction or amplitude of the reach. The results are consistent with the hypothesis that neurons in forelimb regions of interpositus participate in the control of hand movements used in grasping, but they are not consistent with the hypothesis that interpositus neurons participate in direct visual guidance of the limb.

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PubMed1994

The importance of hand use to discharge of interpositus neurones of the monkey.

1. Monkey interpositus neurones show large discharge modulations during reaching to grasp, however, the same neurones show little or no modulation during operation of devices that exercise individual forelimb joints. We tested the hypothesis that grasping during the reach-to-grasp is necessary for eliciting high discharge modulation. 2. Three monkeys (Macaca mulatta) moved an articulated lever between low and high target zones. While in the lower zone the monkey's hand was at its waist, in the upper zone its hand was in a position that required forelimb extension at right-angles to the body axis. Small drawers adjacent to the target zones contained raisins, and the drawers could be remotely opened. Thus, we could elicit two types of reaches having similar trajectories: one reach involved limb transport while holding the lever handle, and the other involved limb transport while forming the hand to grasp a raisin. 3. Eighty-one neurones from two monkeys, mostly from interpositus with some from adjacent regions of dentate, were tested during device use and reaching to grasp: 93% of the neurones discharged at high rates during at least one of the tasks. Of these, about half increased discharge rate solely during reaching to grasp; the other half showed some increase during device use but only discharged strongly during reaching to grasp. Overall, discharge modulations during the reach-to-grasp averaged twice as high as during the corresponding device movement (112 versus 56 impulses s-1). 4. Individual neurones consistently discharged with characteristic patterns during the reach-to-grasp with rates often exceeding 300 impulses s-1. Discharge during the reach-to-grasp was independent of reach trajectory: discharge patterns and amplitudes were similar when reaching from either the lower or upper target zone to the upper raisin drawer as when reaching from the upper target zone to the upper raisin drawer. Reach direction also made little difference: reaches from the upper target zone to the lower drawer typically elicited similar discharge modulation as those from the lower target zone to the upper drawer. 5. High discharge rates associated with grasping were independent of the item being grasped: typically, grasping the device handle elicited as high discharge rates as grasping a raisin. 6. The hypothesis was confirmed that grasping is critical for eliciting high discharge modulation in interpositus during reaching to grasp. Discharge pattern and modulation do not vary with reach direction or amplitude of the reach and, therefore, it is unlikely that intermediate cerebellum controls these features of the reach-to-grasp.(ABSTRACT TRUNCATED AT 400 WORDS)

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PubMed1993

Receptive fields of single cells from the face zone of the cat rostral dorsal accessory olive.

Natural stimulation was used to map the receptive fields of single cells recorded from the rostral medial portion of the dorsal accessory olive (rDAO) and the subjacent principal olive (PO) of the barbiturate anesthetized cat. Previous reports indicated a somatotopic mapping of the entire contralateral body within the rDAO which included a small face zone and a larger zone with a very precise map for the limbs. While concentrating on the face zone of the rDAO we confirmed the previously reported somatotopy (face: rostral and medial; forelimb: caudal and medial; hindlimb; caudal and lateral; and trunk: rostal and lateral) and found a somatotopy within, and adjacent to, the face zone. At the border between rDAO regions representing forelimb and face, cells with forelimb fields were found to lie dorsally to cells with facial fields. Within the rDAO face region, cells with large facial fields lie dorsally to cells with small facial fields. In both cases, the more ventral cells lie in the ventral lamella of the PO, which suggests a functional as well as physical continuity between rDAO and the ventral lamella of the PO. We therefore conclude that the face zone in the rDAO and the face zone in the PO form one continuous and complete map of the face with an orderly progression of receptive fields. Furthermore, we have found that stimulation of the red nucleus can inhibit rDAO cells with facial receptive fields just as it does cells with receptive fields from the rest of the body.

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PubMed1993

Output organization of intermediate cerebellum of the monkey.

1. The goal of this study was to investigate the motor organization of monkey nucleus interpositus (NI) and neighboring regions of the lateral nucleus (NL) by correlating discharge of single neurons with active movements. Neurons were surveyed during free-form movements as well as during operation of six devices that required movement about specific forelimb joints. The paradigm allowed us to test the hypothesis that discharge of individual cells relates to movements about individual joints. 2. One hundred sixty-two isolated nuclear neurons from two monkeys were studied. Eighty-three percent showed large increases in discharge (an average of 3 times resting rate for forelimb neurons) during movement of one body part, either forelimb, hindlimb, mouth/face, or eyes. 3. Anterior interpositus contains neurons related to hindlimb movement in anterior regions and neurons related to forelimb movement in posterior regions. A mouth/face-related area exists in the dorsal-posterior regions and is continuous with a mouth/face area in the dorsal regions of NL. Posterior interpositus (NIP) showed no clear separation between forelimb and hindlimb neurons: forelimb neurons were encountered throughout the nucleus, and hindlimb neurons were encountered in the medial-anterior two thirds. A distinct eye movement area exists in lateral, posterior, and ventral regions of NIP. This area borders regions of NL that also contain eye movement-related neurons. 4. Forelimb interpositus neurons discharged strongly during reach and grasp; discharge rates were recorded for 41 neurons during a stereotyped reach and the average depth of modulation was 149 imp/s. Nineteen neurons that modulated during device tracking were also tested during reaching, and the depth of modulation was much greater during reaching. 5. Fifty-nine forelimb neurons were tested with device tracking. Twenty-seven (46%) produced no audible modulation, regardless of the joint being exercised. The remaining 32 neurons modulated during movement on at least one device (mean depth of modulation = 84 imp/s). Comparison of discharge during use of different devices revealed no strong evidence for device-specific discharge. 6. Discharge modulations during device tracking were phasic, preceded movement, and, for a small number of cells, showed consistent parametric relations to duration, amplitude, and velocity of movement. 7. Despite a clear somatotopy within NI and NL, there is no finer mapping based on active movements about individual joints within forelimb regions. Discharge modulation depends on movements involving the whole limb. Progress in understanding the function of intermediate cerebellum depends on determining the variables required to elicit consistent and high modulation of neural discharge.(ABSTRACT TRUNCATED AT 400 WORDS)

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PubMed1993

Movement-related inputs to intermediate cerebellum of the monkey.

1. The primary goal of this study was to characterize the information about single-joint forelimb movements supplied to intermediate cerebellar cortex by mossy fibers. Discharge of mossy fibers and Golgi cells was studied while monkeys operated six devices that required movements about specific joints. Additional control experiments in anesthetized cats and monkeys established criteria for identification of mossy fibers and Golgi cells. 2. The control experiments demonstrate that mossy fibers can be distinguished from Purkinje and Golgi cells by the waveshapes of their action potentials. Asynaptic activation from the inferior cerebellar peduncle, in combination with histological localization of recording sites in granular layer or subcortical white matter, verified that mossy fibers produce a variety of waveshapes that are characterized by brief initial phases and relatively small amplitudes. The same waveshapes were observed for the mossy fiber recordings from awake monkeys, and many identified mossy fibers had sensory properties similar to those found in the awake animals. From these combined criteria, we conclude that the recordings in the awake animals were from mossy fibers. Golgi cells, recorded exclusively in the granular layer of cerebellar cortex, were characterized by action potentials of longer duration and larger amplitude as compared with mossy fibers, and none were asynaptically activated from the inferior cerebellar peduncle. 3. Units were isolated while the monkeys made free-form and tracking movements. We studied movement-related discharge of 80 mossy fibers and 12 Golgi cells. Mossy fibers showed high modulations during use of at least one of the six manipulanda and had clear preferences for movement about a specific joint, although they often showed consistent but weaker firing during movement about a neighboring joint. Separation of movements by more than one joint produced a large reduction in discharge: shoulder units never fired well to movements of the finger, and finger units never fired well to movement of the shoulder. 4. The tracking task required maintenance of fixed limb positions (a static phase) as well as movements between these positions (a dynamic phase). Of 80 mossy fibers, 18% had purely tonic discharge patterns, 63% were phasic-tonic, and 20% were purely phasic. Discharge patterns were reciprocal (45%), bidirectional (42%), or unidirectional (13%). 5. Eighty percent of the mossy fibers exhibited tonic discharge that was significantly (P < 0.01) correlated with joint angle (r = 0.65 +/- 0.19, mean +/- SD), and about one third had phasic components that were significantly correlated with movement velocity.(ABSTRACT TRUNCATED AT 400 WORDS)

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PubMed1992

Spatial overlap of rubrospinal and corticospinal terminals with input to the inferior olive.

Somatosensory responses of cells in the dorsal accessory olive are suppressed following stimulation of the magnocellular red nucleus. Since the magnocellular red nucleus of the cat does not project directly to the dorsal accessory olive, the present experiments were designed to identify indirect pathways that might mediate suppression of olivary responsiveness. Wheat germ agglutinin-horseradish peroxidase was used to compare the location of magnocellular red nucleus terminals with the locations of cells providing input to the rostral dorsal accessory olive. Cells projecting to forelimb rostral dorsal accessory olive can be divided into two main groups: one group comprises a column of large cells located in the ventral caudal cuneate nucleus extending into lamina VI of C1 and C2, and a second group comprises smaller cells located in the ventral rostral cuneate nucleus. Terminations of fibers originating in the magnocellular red nucleus were found to target both groups of cells projecting to the dorsal accessory olive. Therefore, it is possible that the responsiveness of olivary cells is influenced via these terminations. Stimulation of sensorimotor cortex has also been shown to inhibit olivary responsiveness. Terminations from sensorimotor cortex target the same regions of cells that project to the dorsal accessory olive as those of the magnocellular red nucleus, and a similar, perhaps identical, anatomical substrate may serve to modulate olivary sensitivity by the two descending systems.

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PubMed1991

Decussation of hind-limb and fore-limb fibers in the monkey corticospinal tract: relevance to cruciate paralysis.

Cruciate paralysis is a clinical entity in which patients with trauma to the anterior cervicomedullary junction present with weakness of the upper extremity greater than that of the lower extremity. The underlying mechanism of this paralysis is commonly thought to be selective damage affecting the upper-extremity nerve fibers in the pyramidal decussation. The authors examined the anatomical basis of cruciate paralysis in six New World squirrel monkeys and two Old World cynomolgus monkeys. No evidence for a differential decussation of fore-limb and hind-limb fibers was found. Thus, there is no obvious anatomical explanation for cruciate palsy. The results do suggest two alternative explanations for cruciate paralysis: 1) selective damage to neural areas involving the internuncial cells, the central gray area, and the cuneate nucleus, or 2) injury to the ventral corticospinal tract.

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PubMed1990

Inhibition of sensory responses of cat inferior olive neurons produced by stimulation of red nucleus.

1. The sensory responsiveness of cells in the inferior olive is known to be suppressed during certain phases of active movement. These experiments were designed to test the possibility that activity in the rubrospinal pathway contributes to this suppression. We recorded from cells sensitive to light touch located in one of the divisions of the inferior olive, the rostral dorsal accessory olive (rDAO), in cats anesthetized with pentobarbitol sodium. Responsiveness to peripheral stimuli was tested during and after trains of conditioning stimuli delivered to the rubrospinal pathway. 2. All 44 cells in our sample of rDAO neurons showed an inhibition of responsiveness to peripheral stimuli after conditioning stimulation of the rubrospinal pathway. Typical conditioning trains consisted of 0.2-ms pulses at 200 Hz for 100 ms. The mean current required for a reduction in firing probability to 0.5 was 31 microA. Slight increases in intensity often completely inhibited responses to peripheral stimuli. 3. Inhibition of responsiveness showed a delayed time course. Peak inhibition occurred approximately 50 ms after the last pulse in the conditioning train. In many cases there was no demonstrable inhibition during the conditioning train. Increases of train frequency, train duration, or stimulus intensity produced stronger and broader periods of olivary inhibition. 4. The lowest threshold points for eliciting rDAO inhibition coincided with either the magnocellular red nucleus (RNm) or the rubrospinal tract (RST). Stimulation at RST sites produced inhibition of responses in the contralateral but not in the ipsilateral rDAO. Transection of the RST in the upper brain stem blocked the inhibition produced by red-nucleus stimulation without altering the inhibition produced by tract stimulation caudal to the transection. The inhibitory effects thus appear to be caused by activation of the rubrospinal pathway. 5. The inhibitory timing observed in this study may be appropriate for explaining the suppression of olivary responsiveness to contact that has been observed in awake animals. Bursts of movement-related, red nucleus discharge often cease approximately 50 ms before the end of movement. This timing would allow peak inhibition to develop at approximately the time of contact with an object at the end of a goal-directed limb movement.

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PubMed1987

Selective projections from the cat red nucleus to digit motor neurons.

Classical studies of the cat rubrospinal tract describe dense terminations in spinal laminae V-VII and an absence of any significant projection to lamina IX. In contrast, our recent studies, utilizing the anterograde transport of wheat germ agglutinin conjugated with horseradish peroxidase, have demonstrated a consistent and circumscribed area of label in lamina IX at caudal cervical segments. The present study was undertaken to determine the distribution of rubrospinal terminals among motor neurons in lamina IX as well as to identify the likely target muscles of those motor neurons located near rubrospinal terminals. We injected wheat germ agglutinin-horseradish peroxidase into the red nucleus and unconjugated horseradish peroxidase into selected forearm muscles of the same side of the body. The locations of rubrospinal terminals showing anterograde label on one side of the spinal cord could then be compared with the locations of motor neurons showing retrograde label on the opposite side of the cord. The results demonstrated a clear focus of rubrospinal terminals in the lateral and dorsal portions of the ventral horn beginning at C8 and extending through rostral T1. No other segments of the spinal cord showed a focus of rubrospinal terminations in lamina IX. Retrogradely labeled motor neurons from the muscle injections showed that the rubrospinal terminals overlap extensively with motor neuronal pools supplying distal forearm muscles. Several lines of evidence indicate that the terminals are from rubrospinal fibers and are not due to transneuronal transport.

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PubMed1987

Somatotopic alignment between climbing fiber input and nuclear output of the cat intermediate cerebellum.

The rostral dorsal accessory olive (rDAO) contains a detailed somatosensory map of the entire contralateral body surface. The rDAO projects to the anterior interpositus nucleus (NIA) directly as well as indirectly by way of Purkinje cells in cerebellar cortex. NIA maintains a topographic relation to different levels of the spinal cord through a relay in the magnocellular red nucleus (RNm) and, thus, contains a motor somatotopy. By using bidirectional transport of WGA-HRP, we demonstrate that the sensory somatotopy of rDAO aligns with the motor somatotopy of NIA. It is likely that rDAO information supplied to the cerebellum from a specific part of the body is used to influence movements restricted to that same body part.

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