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Biomedical subjects

G Mandl

Publications and source records attributed to G Mandl.

5 recordsLinked to original sources
PubMed1978

Frontal 'oculomotor" area in alert cat. I. Eye movements and neck activity evoked by stimulation.

(1) Stimulation within cat frontal lobe elicited saccadic eye movements whose maximum velocity was significantly greater than that of normal spontaneous saccades. (2) The majority (90%) of stimulated cortical points yielded eye movements whose directions and amplitudes were independent of the position of the eye in the orbit. The direction of these eye movements depended on the site being stimulated, with a discrete and orderly representation of directions existing within the cortex. (3) A lesser number of cortical points (10%) yielded centering movements whose directions and amplitudes depended on the position of the eye in the orbit, rather than on the site being stimulated. (4) Evoked neck muscle activation frequently preceded evoked eye movements by some 15--30 msec. This timing was compatible with a coordinated head-eye orientating response. (5) On the basis of the directions, and the latencies, of evoked eye movements, the cat frontal oculomotor area could be divided into two subregions, a 'medial' and a 'lateral', (6) The 'medial' area included the mesial wall of the hemisphere with a portion of the lower lip of the cruciate sulcus, and the medial wall of the presylvian sulcus. This area yielded contraversive eye movements with shorter latencies (average 45 msec). (7) The 'lateral' area included primarily the lateral wall of the presylvian sulcus. It yielded predominantly centering eye movements, and ipsiversive movements with longer latencies (65 msec). (8) The functional characteristics of the 'medial' area, as revealed by focal stimulation, resembled those of the monkey frontal eye field.

Animals↗
PubMed1978

Frontal 'oculomotor' area in alert cat. II. Unit discharges associated with eye movements and neck muscle activity.

(1) Unit activity in front 'oculomotor' cortex was recorded extracellularly from sites where subsequent electrical stimulation, using threshold current (50 microamperes), could elicit both eye movements and simultaneous neck EMG acitivity. (2) Of 103 cells, 19% were related to either eye movements or neck EMG activity. Cells could be grouped into three categories: (a) Directional (D) cells (31%) discharged before and during saccadic eye movements, whenever the eyes followed a target in one specific direction. Spontaneous saccades, or vestibularly driven nystagmus, in either the light or dark, elicited no responses. (b) Conditionally directional (CD) cells (43%) discharged following (i) tracking saccades; (ii) spontaneous saccades and (iii) the quick phase of nystagmus, in all directions. There usually was a slight discharge preference for one given direction, and this preference was enhanced whenever visual tracking was restricted to the preferred direction. One-third of CD cells responded to stimulation of the contralateralal biventer cervicis neck muscle (min lat. 20 msec). (c) Neck EMG (N) cells (26%) discharged in association with, and preceding, changes in neck muscle activity. These cells also responded to stimulation of the contralateral biventer cervicis muscle (min lat. 10 msec). (3) For points in the lateral 'oculomotor' region (as defined by stimulation: see ref. 17), the directions of evoked saccades, and the directions of spontaneous saccades associated with unit discharges, were sililar. In the medial region 17, the directions of evoked saccades were roughly opposite to the directions of spontaneous eye movements favoured by unit discharges.

Action Potentials↗