Saccade modulation by optical and electrical stimulation in the macaque frontal eye field

Area of Science:

• Neuroscience
• Optogenetics
• Motor Control

Background:

• Optogenetic stimulation in macaque motor cortex can modulate neural activity without causing movement.
• The reasons for this lack of movement and conditions that might evoke it remain unclear.

Purpose of the Study:

• To investigate the effects of optogenetic constructs in the macaque frontal eye field.
• To determine if optical perturbation combined with electrical stimulation evokes motor changes.

Main Methods:

• Tested five optogenetic constructs in macaque frontal eye field.
• Used electrical microstimulation for optical, electrical, and combined stimulation.
• Conducted simultaneous fMRI with channelrhodopsin 2 (ChR2) and electrical stimulation.

Main Results:

• Combined optical and low-current electrical stimulation significantly increased saccadic eye movement probability compared to electrical stimulation alone.
• fMRI showed no discernible activity at the electrode tip with optical stimulation, but strong activity with electrical stimulation.
• Optogenetic stimulation generated subthreshold activity contributing to movement initiation.

Conclusions:

• Current optogenetic constructs often produce subthreshold activity insufficient to evoke motor responses.
• Combining optogenetics with electrical stimulation can enhance motor output probability.
• Further research is needed to understand the precise mechanisms of optogenetic control over motor output.