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Edward J. Tehovnik, Warren M. Slocum, Peter H. Schiller; Electrical properties of elements mediating saccadic eye movements within macaque V1: excitability differences between layers. Journal of Vision 2002;2(7):158. doi: 10.1167/2.7.158.
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© ARVO (1962-2015); The Authors (2016-present)
Electrical stimulation of superficial V1 (layers I through IV) interrupts a monkey's ability to select visual targets appearing in the receptive field region of the stimulated neurons, whereas stimulation of the deep V1 (layers V and VI) tends to drive the eyes toward the target (Schiller and Tehovnik 2001). Given this functional segregation between layers, we performed experiments to assess the excitability of neural elements activated while inducing saccadic eye movements electrically from different cortical layers of V1 in the rhesus monkey. Using cathodal-first stimulation, saccades could not be evoked from the surface of V1 using currents as high as 30 uA. The current threshold to evoke saccades, however, dropped to between 2 and 3 uA as the electrode was advanced between 1.5 and 2.0 mm below the cortical surface. The minimum latency at which saccades were evoked from V1 using suprathreshold currents that were 10 times threshold ranged from 48 to 55 ms. The chronaxies of the directly-stimulated elements mediating saccades in V1 ranged from 0.12 to 0.41 ms, with elements in superficial V1 exhibiting longer chronaxies than those of deep V1. Anodal-first pulses were more effective than cathodal-first pulses at evoking saccadic eye movements from superficial V1, while cathodal-first pulses were most effective at evoking saccades from deep V1. Our chronaxie estimates and the anode-cathode ratio values obtained for evoking saccades from V1 are similar to those reported for elements mediating phosphenes in humans.
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