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Biomedical subjects

J Schlag

Publications and source records attributed to J Schlag.

At least 55 records · Page 3Linked to original sources
PubMed1980

Visuo-oculomotor properties of cells in the superior colliculus of the alert cat.

Visual responses and eye movement (EM) -related activities were studied in single units of the superior colliculus (SC) of alert cats. Spontaneous EMs were encouraged by training. Throughout the SC (i.e., in intermediate and deep layers as well as in superficial layers), units were found to respond well to visual stimuli. Strong and consistent responses could be elicited by very dim, low-contrast stationary stimuli. Visual responses varied from phasic to tonic; some units responded tonically to stationary stimuli in the center of the receptive field, and phasically to peripheral stimuli. Many cells responded more vigorously to moving than to stationary stimuli, but very few responded exclusively to stimulus movement. The vast majority of cells were directionally selective. A small number of units were sensitive to the absolute, as well as the retinal, position of visual stimuli. These cells were activated by visual stimuli which fell in the receptive field only if the cat's gaze was fixated on one half of the screen. It seems that these cells must receive information about both eye position and the retinal (receptive field) position of the stimulus. It is possible that they reflect coding of target location within a head (or body) frame of reference. EM-related units were of two types: (1) about 20% of the sample responded prior to spontaneous or visually-triggered EMs, and (2) another 10% (or more) responded with, but not before, EMs. Some cells in the second group discharge almost synchronously with EMs and, thus, cannot plausibly be said to respond to the movement of images across the retina. All cells in the first group were directionally selective. The percentage of EM-related cells in the deep layers of SC is lower in cat than in monkey. Possible reasons for such differences are discussed.

Animals↗
PubMed1980

Visual responses of thalamic neurons depending on the direction of gaze and the position of targets in space.

Visual receptive field properties of neurons in the region of the thalamic internal medullary lamina were studied in alert cats while they fixated in various directions. In slightly more than 50% of the cells, the responsiveness of the cells was found to depend on the location of the stimulus with respect to the head-body axis (stimulus absolute position). A cell could ignore a stimulus outside its absolute field even if it was well placed within its receptive field. Three types of neurons were distinguished. Neurons with small central receptive fields were tonically activated when the animal fixated the stimulus in one half of the screen (usually contralateral). The firing rate of these cells was related to the stimulus absolute position measured along a preferred axis. Similarly, neurons with large receptive fields fired as a function of stimulus absolute position but stimulus fixation was not required. Neurons with eccentric fields responded to stimuli located in a target area defined in head-body coordinates. Such cells gave presaccadic bursts with eye movements terminating in the target area. The conclusion proposed is that neurons exist which code visual spatial information in a non-retinal frame of reference. This coding takes place at the time of stimulus presentation. Its role may be seen in the initiation of visually guided movements.

Animals↗
PubMed1977

Visual and presaccadic neuronal activity in thalamic internal medullary lamina of cat: a study of targeting.

1. Visual responses and eye movement-related activities were studied in single neurons of the thalamic internal medullary lamina (IML) of alert cats. The animals faced a tangent screen on which stationary or moving spots of light were presented. Of 95 units, 26% discharged in relation to photic stimuli but not eye movement, 6% in relation to eye movement but not photic stimuli, and 68% in relation to both. These units were intermixed in the same region. 2. Visual responses varied from transient to sustained. IML units were not found particularly sensitive to stimulus movement when the eyes were fixed. Strong and consistent responses could be elicited by extremely dim and weakly contrasted stationary stimuli (e.g.) 3.4 mcd/m2, 2.6% of illumination background) binocularly viewed. Receptive fields (from 250 to 800 deg2) were determined, in absence of eye movements, by computing the position of effective stimuli relative to the point of fixation of the gaze. An area of greatest responsiveness in the receptive field of most units could be detected on the basis of either higher probability of response, minimum latency, greater number of spikes in initial transient burst, or stronger sustained activity. Whole fields or their areas of greatest responsiveness were located on the side toward which saccades were accompanied by increased firing of the unit. 3. On trials in which a delay occurred between stimulus presentation and the cat's targeting saccade, the majority of the units studied changed their activity twice: after the stimulus and before the eye movement. In 16 units, the presaccadic activation occurred only with targeting, not with spontaneous saccades. 4. These results suggest that cells in the IML region of the cat play a significant role in the control of visually elicited eye movements. The resemblance of these cells to the monkey's tectual cells is discussed and hypotheses are proposed a) to relate the receptive field characteristics to the targeting operation, and b) to account for the double activation--sensory and motor--of many IML cells.

Animals↗