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Biomedical subjects

C W Mohler

Publications and source records attributed to C W Mohler.

9 recordsLinked to original sources
PubMed1981

Long-term evaluation of patients with Best's vitelliform dystrophy.

We examined 91 patients with Best's dystrophy and followed 54 affected individuals for five years. Most eyes with normal maculas, minimal pigment epithelial changes, atrophic maculae, or fibrous macular scars did not change stage. Eyes with vitelliform or pseudohypopyon lesions progressed to later atrophic macular stages. Visual acuity decreased after age 40 and was worse for patients with atrophic maculas and fibrous scars. Nineteen percent of patients with atrophic maculas or fibrous scars who were followed for 8 to 10 years were the only patients to lose vision.

Adult↗
PubMed1977

Role of striate cortex and superior colliculus in visual guidance of saccadic eye movements in monkeys.

1. We studied the effect of lesions placed in striate cortex or superior colliculus on the detection of visual stimuli and the accuracy of saccadic eye movements. The monkeys (Macaca mulatta) first learned to respond to a 0.25 degrees spot of light flashed for 150-200 ms in one part of the visual field while they were fixating in order to determine if they could detect the light. The monkeys also learned in a different task to make a saccade to the spot of light when the fixation point went out, and the accuracy of the saccades was measured. 2. Following a unilateral partial ablation of the striate cortex in two monkeys they could not detect the spot of light in the resulting scotoma or saccade to it. The deficit was only relative; if we increased the brightness of the stimulus from the usual 11 cd/m2 to 1,700 cd/m2 against a background of 1 cd/m2 the monkeys were able to detect and to make a saccade to the spot of light. 3. Following about 1 mo of practice on the detection and saccade tasks, the monkeys recovered the ability to detect the spots of light and to make saccades to them without gross errors (saccades made beyond an area of +/-3 average standard deviations). Lowering the stimulus intensity reinstated both the detection and saccadic errors...

Animals↗
PubMed1976

Organization of monkey superior colliculus: intermediate layer cells discharging before eye movements.

1. We investigated the characteristics of cells in the intermediate layers of the superior colliculus that increase their rate of discharge before saccadic eye movements. Eye movements were repeatedly elicited by training rhesus monkeys to fixate on a spot of light and to make saccades to other spots of light when the fixation spot was turned off. 2. The eye movement cells showed consistent variations with their depth within the colliculus. The onset of the cell discharge led the eye movement by less time and the duration of the discharge was shorter as the cell was located closer to the dorsal edge of the intermediate layers. The movements fields (that area of the visual field where a saccade into the area is preceded by a burst of cell discharges) of each successive cell also became smaller as the cells were located more dorsally. The profile of peak discharge frequency remained fairly flat throughout the movement field of the cells regardless of depth of the cell within the colliculus. 3. A new type of eye movement-related cell has been found which usually lies at the border between the superficial and intermediate layers. This cell type, the visually triggered movement cell, increased its rate of discharge before saccades made to a visual stimulus but not before spontaneous saccades of equal amplitude made in the light or the dark. A vigorous discharge of these cells before an eye movement was dependent on the presence of a visual target; the cells seemed to combine the visual input of superficial layer cells and the movement-related input of the intermediate layer cells. The size of the movement fields of these cells were about the same size as the visual fields of superficial layer cells just above them...

Action Potentials↗
PubMed1976

Organization of monkey superior colliculus: enhanced visual response of superficial layer cells.

1. Cells in the superficial layers of monkey superior colliculus respond more vigorously to a spot of light falling in their receptive fields when the monkey uses that spot of light as the target for a saccadic eye movement. Our purpose in these experiments was to investigate the characteristics of this enhancement effect. While monkeys fixated, we determined the response of a cell to a stimulus falling in its receptive field. Then we determined the response of the cell to the same stimulus when the monkey made a saccade to the stimulus or near to it. 2. The enhancement of the visual response is spatially limited. The receptive field of a cell always shows enhancement throughout its extent and frequently shows a slight expansion. Saccades made near to a stimulus in the visual receptive field, but not to it, also lead to an enhancement of that visual stimulus; an area around the excitatory center of the receptive field where such enhancement occurs was referred to as the enhancement field of the cell. An enhanced response in one part of the visual field was not accompanied by depressed responses associated with saccades to other parts of the visual field. 3. The enhancement effect is temporally limited; it begins 200-300 ms before the eye movement, as determined by the increasing response to 50-ms light pulses presented at varying intervals before the eye movement. The degree of enhancement intensifies when the visual stimulus is turned on closer in time to the onset of the saccade. A buildup of the enhancement also occurs on successive trials as does the response of eye movement-related cells in the intermediate layers. 4. The enhancement response is not present in the upper quarter-millimeter of the superficial layers, suggesting that the effect is not present in retinal afferents which terminate primarily in this area of the superficial layers. The enhancement effect is seen throughout the visual field; the foveal area was not tested. 5. In order to determine the relation of the enhancement effect to the monkey's behavioral response, we required the monkey to make a hand response rather than an eye movement-response to the visual stimuli. Cells did not show a clear enhancement with such a hand response. Results of these experiments indicate that the enhancement effect is dependent on the type of response the monkey makes to the stimulus and is probably specifically related to eye movements. Since the enhancement of visual response seems likely to be related specifically to eye movements both on physiological and behavioral grounds, the response-free term "attention" is probably inappropriate for the phenomenon. 6. The hypothesis advanced in the preceding paper that eye movement-related activity from intermediate and deep colliculus layers is directed upward to converge with visually related activity in the superficial layers is extended to include an input from cells in these deeper layers (or their afferents) to the superficial layer cells...

Animals↗
PubMed1976

Enhancement of visual responses in monkey striate cortex and frontal eye fields.

1. We have studied the visual enhancement effect in two areas of the cerebral cortex of monkeys. The response of the cells to a visual stimulus was determined both when the monkey used the visual stimulus as the target for a saccadic eye movement and when he did not. 2. In striate cortex cells with nonoriented, simple, complex, and hypercomplex receptive-field types were studied. Clear enhancement of the response to the appropriate visual stimulus was seldom seen when the monkey used the stimulus as a target for a saccade. In addition, any enhancement effect seen was nonselective; it occurred whether the monkey made a saccade to the receptive-field stimulus or some other stimulus at a point distant from the receptive field. The enhancement also occurred whether the monkey made a saccade to the stimulus or just released the bar when the stimulus dimmed. 3. This nonselective enhancement in striate cortex is in striking contrast to the selective enhancement of the visual response seen in the superior colliculus. The different characteristics of the enhancement in striate cortex and the observation of enhancement in the colliculus following ablation of striate cortex suggest that this cortical area is an unlikely source of the collicular enhancement. 4. These observations reinforce the distinction between striate cortex and superior colliculus. Striate cortex is an excellent analyzer of stimulus characteristics but a poor evaluator of stimulus significance. The superior colliculus is an excellent evaluator but a poor analyzer. 5. The area of frontal eye fields in which cells have clear visual responses has been better localized. Enhancement of the visual response of these cells also occurs and, at least for some cells, the response enhancement is selective. The response enhancement, like the visual properties of these frontal eye field cells, appears to be more closely related to the properties of superior colliculus cells than to striate cortex cells.

Animals↗