Distinct Cortical Circuit Mechanisms for Complex Forelimb Movement and Motor Map Topography

Abstract

Cortical motor maps are the basis of voluntary movement, but they have proven difficult to understand in the context of their underlying neuronal circuits. We applied light-based motor mapping of Channelrhodopsin-2 mice to reveal a functional subdivision of the forelimb motor cortex based on the direction of movement evoked by brief (10 ms) pulses. Prolonged trains of electrical or optogenetic stimulation (100-500 ms) targeted to anterior or posterior subregions of motor cortex evoked reproducible complex movements of the forelimb to distinct positions in space. Blocking excitatory cortical synaptic transmission did not abolish basic motor map topography, but the site-specific expression of complex movements was lost. Our data suggest that the topography of movement maps arises from their segregated output projections, whereas complex movements evoked by prolonged stimulation require intracortical synaptic transmission.

Optogenetic Analysis of Neuronal Excitability during Global Ischemia Reveals Selective Deficits in Sensory Processing following Reperfusion in Mouse Cortex

“…The nature of the ChR2-mediated electrophysiological signal The ChR2-mediated EEG or LFP response can reflect both direct ChR2-mediated and indirect synaptic activation, and can last longer than the duration of the light stimulus (Harrison et al, 2012;Lim et al, 2012). Given the relatively long deactivation time for ChR2 (Fenno et al, 2011), even the response to direct activation should be on the order of 10 -15 ms in duration, consistent with the peak responses we observe.…”

“…1Cii). Brief 5 ms pulses of 473 nm light produced a depolarizing EEG response that contained components expected from rapid (within 15-25 ms) direct ChR2 activation (Ayling et al, 2009), as well as delayed responses that may reflect secondary activation of neurons through synaptic transmission (Harrison et al, 2012;Scott and Murphy, 2012). During baseline EEG recordings (15-40 min before CCAO), the ChR2 response peak from each 5 ms 473 nm laser stimulation pulse was 0.5-2 mV and occurred ϳ15-25 ms after stimulation.…”

Mesoscale infraslow spontaneous membrane potential fluctuations recapitulate high-frequency activity cortical motifs

“…Importantly sham drug application was used for comparison and to control against nonspecific time-dependent effects. TTX and glutamatertigic receptor antagonist treatment in this manner previously blocked cortical activity in all the layers 68,69 .…”

What single-cell stimulation has told us about neural coding

“…Interestingly, application of long electrical or optogenetic stimulation currents of high intensities evokes complex movements in primates, cats and rodents [10,[116][117][118][119][120][121]. Moreover, recent studies compared the effects of optogenetic stimulation of motor and sensory cortices pyramidal neurons with those of ICMS and surprisingly found that both methods produced similar sensations and movements, suggesting that they might influence the neural activity of the circuit in a similar fashion [122,123]. The comparison of the motor effect of single-cell stimulation and microstimulation in the rat motor cortex led to quite unexpected results.…”