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L T Robertson

Publications and source records attributed to L T Robertson.

30 records · Page 2Linked to original sources
PubMed1982

Organization of climbing fiber input from mechanoreceptors to lobule V vermal cortex of the cat.

The somatotopic organization of the climbing fiber (CF) projections to the vermal cortex of lobule V of the cat was revealed by low threshold natural stimulation of mechanoreceptors. Extracellular single-unit recordings were made from 554 Purkinje cells in cats anesthetized with sodium pentobarbital. Forty-nine percent of the CF responses were elicited by cutaneous stimulation of the forelimb (62%), hindlimb (25%), or upper back and neck (13%). The topographical arrangement consisted of a 1 mm wide medial zone and a 1-1.5 mm wide lateral zone. In the medial zone, the CF responses were mainly nonresponsive to any cutaneous stimulation except in the caudomedial portion of the lobule where the upper back, neck or ears were represented in a narrow parasagittally oriented strip. The lateral zone contained a mixture of CF responses representing projections from different portions of the ipsilateral forelimb and hindlimb. Although CF responses connected with the forepaw or hindpaw predominated throughout all parts of the lateral zone, the more medial portions of this zone contained larger receptive fields involving the more proximal areas of the limb whereas the lateral part of the zone had smaller receptive fields representing the distal regions, particularly the ventral forepaw surface. Cells with similar receptive fields were often grouped together, but adjacent skin areas were not necessarily represented in adjacent cortical patches. Thus, the cutaneous projections to this lobule terminated in a patchy or mosaic fashion.

Animals↗
PubMed1981

Localization of cutaneously elicited climbing fiber responses in lobule V of the monkey cerebellum.

The somatotopic organization of climbing fibers (CF) elicited by natural stimulation was determined for the intermediate zone of lobule V of Macaca fascicularis. In monkeys anesthetized with sodium pentobarbital, extracellular recordings of single Purkinje cells with CF responses were evaluated by gentle taps to the body and by computer-controlled punctate stimuli. Of the 311 Purkinje cells studied, 53% had CF responses elicited by cutaneous stimulation whereas the remaining cells were unresponsive. The entire ipsilateral, dorsal surface of the forelimb, face, and the oral cavity were represented in the intermediate zone. The topographic organization consisted of three 1.5-3 mm wide parasagittal bands of cells: a forelimb band medially, then a face band, and an unresponsive zone laterally. Most receptive fields in the forelimb band involved portions of the wrist, hand, and digits, although shoulder, arm, and forearm were also represented. The receptive fields of the hand usually included more than 1 digit and only a few fields contained the thumb. Most responses in the face band were elicited by stimulation of areas innervated by the mandibular division of the trigeminal nerve, although some responses were produced by stimulating areas related to the ophthalmic and maxillary divisions and to the anterior cutaneous nerve. Cells with similar receptive fields tended to be grouped together. The somatotopic CF organization of the monkey differed in many ways from the arrangement in the cat.

Afferent Pathways↗
PubMed1980

Somatotopic organization of climbing fiber projections from low threshold cutaneous afferents to pars intermedia of cerebellar cortex in the cat.

The fine detail of climbing fiber projections to large areas of the pars intermedia of lobule V was demonstrated by means of low threshold natural cutaneous stimulation. These projections formed a complex mediolateral organization of patches that were elongated in the anteroposterior direction. In general, distal forelimb was represented medially and the face represented laterally, although there were also elongated patches of cells that did not respond to any cutaneous stimulus presentation. The entire ipsilateral anterior quadrant of the body was represented in lobules Vb, c, d with the addition of face projections which extended slightly across the midline. Ipsilateral hindlimb patches were observed in lobule Va. Although the boundary between patches was quite sharp, a slight overlap of the patches within the mosaic was often observed. In these areas of overlap, some cells possessed receptive fields that encompassed, either continuously or discontinuously, cutaneous areas of both the adjacent patches. It is proposed that the cerebellar cortex could correlate event timing in the climbing fiber patches with 'on-line' information relating the parameters of movement in the granule cell parallel fiber system, and that the areas described in the present study could mediate 'spatially organized and skilled movements' in the animal's repertoire, which involve paw-face-mouth interaction, such as feeding, cleaning and grooming.

Afferent Pathways↗
PubMed1980

Speech changes in cerebral-palsied patients after cerebellar stimulation.

A quantitative study was made of the effects of focal cerebellar stimulation on oral-motor control, duration of phonation, articulation and vocal characteristics in 10 patients with cerebral palsy. The patients were evaluated prior to surgery and again after approximately two and six months of cerebellar stimulation. One patient had normal speech, which was not affected by the stimulation; another case with moderate dysarthria due to severe hearing loss was not helped by the stimulation. Seven patients increased their duration of vowel phonation by about two seconds, a significant amount. Four of the patients with moderate dysarthria improved their articulation, particularly for the consonants S, Sh and Th, after two months of stimulation. Two patients had changes in oral-motor control, which included better tongue and lip movements, and two other cases had small alterations in hypernasality or breathiness. Most of the changes in sound production and speech intelligibility appear to be related to improved intra-oral breath control.

Adolescent↗
PubMed1980

Physiological and behavioral changes produced by cerebellar stimulation in the monkey.

Small surface electrodes were placed bilaterally over the intermediate or lateral cerebellar cortex of cynomolgus monkeys to determine how electrical stimulation of different areas of the cerebellar cortex affected average evoked responses and a sequential forelimb movement. Biphase electrical stimulation was applied between various electrode combinations, and various intensities and frequencies were established for each combination. Transcortical stimulation between the right and left intermediate cerebellar cortex required the lowest intensity (1.5 microC/sq cm/ph) to elicit an average evoked response in the sensorimotor cortex; stimulation between the electrodes over the contralateral intermediate or lateral cortex required slightly higher levels (2.0 microC/sq cm/ph). No response could be elicited from stimulating the ipsilateral cortex. Likewise, 1 minute of transcortical stimulation was more effective than comparable stimulation of the contralateral intermediate or lateral cortex in altering the waveforms of a somatosensory evoked response. Transcortical stimulation also modified the forelimb movement, whereas contralateral stimulation of the intermediate or lateral cortex had little or no effect. Transcortical stimulation at 2.0 microC/sq cm/ph, with frequencies of 150 Hz or higher, increased the time required to execute the forelimb movement but did not affect the accuracy of the movement. High-speed motion pictures indicated that transcortical stimulation decreased the velocity of forelimb movement and in some cases also affected the limb trajectory. These results indicate that consideration should be given to the area of the cerebellum stimulated and to the mode of stimulation, in the hope of achieving optimum clinical benefit.

Animals↗
PubMed1980

Longitudinal study of phenobarbital in serum, cerebrospinal fluid, and saliva in the dog.

Serial assays for phenobarbital were done on the blood serum, cerebrospinal fluid (CSF), and saliva from three epileptic and two clinically normal dogs that were given various oral doses of the drug. In all dogs, the three fluids showed considerable daily fluctuations of phenobarbital concentrations, even after several weeks at the same dosage. The average ratio for CSF/serum was 0.53 and 0.39 for saliva/serum. A highly significant (P less than 0.001) correlation coefficient occurred between CSF and serum (0.95) and between CSF and saliva (0.93); although in some dogs at particular dosages, the CSF and saliva were poorly correlated. Dose-related curves demonstrated a gradually increased phenobarbital concentration in the three fluids up to dosages of 9.0 mg/kg of body weight. The present study suggests that multiple serum or saliva samples should be assayed to account for daily fluctuations; saliva can be a good indicator of unbound phenobarbital concentration in CSF.

Animals↗
PubMed1975

Responses of primate dentate neurons to different trajectories of the limb.

The activity of neurons in the dentate nucleus of the squirrel monkey was studied during the execution of a controlled, sequential movement that required different trajectories of the forearm. Examination of 207 dentate neurons ipsilateral to the performing limb revealed that over 80% of the neurons isolated were distinctly correlated with performance. The majority of these neurons had a tonic discharge pattern that usually increased coincident with the start of the movement and was maintained throughout most of the performance. A smaller group of cells ahd a burst of activity that was restricted only to a narrow part of the performance. About 30% of the tonic neurons altered their pattern of discharge whenever different limb trajectories were required, but burst cells showed exxentially no change. Detailed analysis of spike patterns revealed that no dentate neurons were phasically correlated with individual flexion-extension cycles of the performance sequence. Dentate neurons appear to be related to some general function of motor performance rather than the actions of joints or muscles used to execute the task.

Animals↗