Depth‐dependent detection of microampere currents delivered to monkey V1

Abstract

Monkeys can detect electrical stimulation delivered to striate cortex (area V1). We examined whether such stimulation is layer dependent. While remaining fixated on a spot of light, a rhesus monkey was required to detect a 100 ms train of electrical stimulation delivered to a site within area V1. A monkey signaled the delivery of stimulation by depressing a lever after which he was rewarded with a drop of apple juice. Control trials were interleaved during which time no stimulation was delivered and the monkey was rewarded for not depressing the lever. Biphasic pulses were delivered at 200 Hz and the current was typically at or less than 30 μA using 0.2 ms cathode-first biphasic pulses. For some experiments, the pulse duration was varied from 0.05 to 0.7 ms and anode-first pulses were used. The current threshold for detecting cathode-first pulses 50% of the time was the lowest (< 10 μA) when stimulation was delivered to the deepest layers of V1 (between 1.0 and 2.5 mm below the cortical surface). Also the shortest chronaxies (< 0.2 ms) and the shortest latencies (< 200 ms) for detecting the stimulation were observed at these depths. Finally, anode-first pulses were most effective at evoking a detection response in superficial V1 and cathode-first pulses were most effective at evoking a detection response in deep V1 (> 1.75 mm below the cortical surface). Accordingly, the deepest layers of V1 are the most sensitive for the induction of a detection response to electrical stimulation in monkeys.

New methods devised specify the size and color of the spots monkeys see when striate cortex (area V1) is electrically stimulated

“…The initial experiments carried out by Robert Doty and his colleagues (15)(16)(17)(18) on monkeys established beyond a doubt that monkeys can detect electricity delivered to area V1 (19)(20)(21)(22)(23)(24)(25)(26)(27). These experiments also established that similar groups of neurons in area V1 are activated in both monkeys and humans for the generation of phosphenes (16,19,23).…”

“…These experiments also established that similar groups of neurons in area V1 are activated in both monkeys and humans for the generation of phosphenes (16,19,23). What remains unanswered is what the visual characteristics are of phosphenes evoked from monkey area V1.…”

“…Recordings were made to map out the location of the receptive field at the tip of the electrode while the monkey maintained fixation on a small spot in the center of the computer monitor that the animal was facing (19,25,28,29). We then performed electrical stimulation to establish effective thresholds for eliciting saccadic eye movements that shifted the center of gaze from the fixation spot into the receptive field location of the stimulated neurons.…”

Differences of Intracranial Electrical Stimulation Thresholds in the Human Brain

“…Within the cerebral cortex the sixth cortical layer requires the least current strength for eliciting clinical symptoms [10,11].…”

Microelectrode array stimulation combined with intrinsic optical imaging: A novel tool for functional brain mapping

“…In addition to mapping, electrical microstimulation has proven useful for controlled modulation of sensory percepts and behaviors (6-10) and for brain-machine interface applications (11, 12). However, despite the exciting advances in brain stimulation technology, the understanding of circuits underlying these behavioral effects remains indirect and limited.…”