Sparse optical microstimulation in barrel cortex drives learned behaviour in freely moving mice.

Area of Science:

• Neuroscience
• Optogenetics
• Cortical circuits

Background:

• Electrical microstimulation is crucial for linking neural activity to cognition, but lacks precision in controlling neuron numbers and action potentials.
• Channelrhodopsin-2 (ChR2), a light-gated ion channel, offers a potential solution for targeted neuronal activation.

Purpose of the Study:

• To investigate the minimum number of neurons and action potentials required to drive perceptual learning and decisions.
• To assess the efficacy of ChR2-mediated photostimulation in activating specific cortical circuits.

Main Methods:

• ChR2 was specifically introduced into a sparse population of layer 2/3 neurons in the mouse primary somatosensory cortex.
• In vivo photostimulation was used to evoke stimulus-locked action potentials at various frequencies.
• Naive mice were trained to detect ChR2-evoked photostimuli.

Main Results:

• ChR2 photostimulation reliably generated action potentials up to 50 Hz.
• Mice learned to detect photostimuli involving as few as approximately 300 neurons for brief stimuli (single action potential).
• Detection thresholds decreased further with longer stimuli, requiring approximately 60 neurons for five action potentials over 250 ms.

Conclusions:

• Perceptual decisions and learning can be driven by remarkably brief and sparse epochs of cortical activity.
• A small subset of supragranular cortical pyramidal neurons is sufficient to mediate behavioral responses.
• Optogenetic control of neural activity provides a powerful tool for studying the neural basis of cognition.