Multiple-Color Optical Activation, Silencing, and Desynchronization of Neural Activity, with Single-Spike Temporal Resolution

Causal Control # Continue PAPER_TPL BIO

Yellow light drives Halo to silence spikes with high temporal precision; blue light can excite via ChR2, enabling bidirectional, targeted causal control.

"In total, during periods when the yellow light was off, somatic current pulses elicited spikes 98.7% of the time, whereas during periods when the yellow light was on, somatic current pulses elicited spikes only 1.2% of the time. The temporal precision of Halo in silencing spikes therefore offers a novel method of creating ultratransient, precise, and effective inhibition of activity in genetically-specified neurons."

RESULTS, p. 4

Result shows direct, temporally precise, causal control of neuronal spiking via light-gated chloride pumping, establishing a powerful intervention modality relevant for testing consciousness-linked computations in brain circuits .

"Even a brief pulse of yellow light could completely silence the spiking of a Halo-expressing neuron, and yet allow normal spiking activity within milliseconds after light cessation. Furthermore, individual neurons could express the yellow light-activated chloride pump Halo and the blue-light activated cation channel ChR2, and respond to yellow vs. blue light with oppositely-directed voltage changes."

DISCUSSION, p. 8

Authors summarize bidirectional, rapid causal control over neural activity—an essential capability for interventional tests of theories of consciousness and for mapping computation to report and access pathways .

Figures

Fig. 4 (p. 6) : Figure demonstrates precise, light-timed spike blockade, highlighting the effectiveness and temporal specificity of causal intervention in single neurons—key for dissecting the neural basis of conscious processing .

Limitations: Findings are in vitro in cultured hippocampal neurons rather than behaving animals; downstream effects on perception or report are not measured; opsin rundown and optical delivery constraints may limit duration or tissue penetration in vivo .

Temporal Coordination # Continue PAPER_TPL BIO

Two-color optical control perturbs precise spike timing while preserving spike rate, enabling targeted desynchronization without rate confounds.

"optically driving Halo and ChR2 could sometimes abolish previously reliable spikes, create new spikes, or advance or delay the timing of specific spikes. We compared mean spike rates ... and found no difference in spike rates for these two conditions ... However, precise spike timing was altered significantly: cross-correlations ... were on average 37% smaller than cross-correlations of pairs of spike traces resulting from Gaussian current injections alone."

RESULTS, p. 8

Demonstrates selective disruption of temporal precision (phase/timing) while holding rate constant—an experimental handle on synchrony and timing mechanisms implicated in conscious access and binding .

Figures

Fig. 7 (p. 8) : Caption and data show desynchronization of spike timing with preserved rates, directly probing temporal coordination mechanisms relevant to conscious processing .

Limitations: Experiments are limited to single-neuron recordings in culture, not network-scale oscillations in vivo; thus, generalization to large-scale temporal coordination (e.g., cross-area phase coupling) remains to be tested .