Optogenetically stimulating the motor cortex with a transparent skull

Previous efforts to use optogenetics to map various behaviors in the brain has been limited by the fact that scientists could not vary the location of the photostimulated area. Additionally, the technique of delivering light via an optical fibre is invasive and prohibits free movement. Hira et al (2009) have taken a step towards overcoming these difficulties by coating the surface of the transgenic mice skull with clear acrylic dental resin in order to keep it transparent. By administering brief (4 ms) pulses of blue light to regions of the motor cortex, they rapidly induced time-locked limb movement for at least 10 trials in a row.

By stimulating either the left or right hemisphere of the motor cortex, they were able to induce movement in either the right or left limbs, respectively. They then stimulated the brain in different regions within each hemisphere to determine specific spatial correlates. In both hemispheres they found that stimulating the motor cortex area that led to forelimb movement was rostral to the region that controlled for hindlimb movement, which is corroborated by earlier research. Their in vivo method allows for photostimulation of channelrhodopsin neurons in any spatiotemporal pattern, which will probably be exploited in a number of creative ways. Some sort of open-field learning paradigm manipulation piggybacking on Airan et al and photostimulating neurons in the nucleus accumbens seems like a ripe application.

Reference

Hira R, et al. 2009 Transcranial optogenetic stimulation for functional mapping of the motor cortex. Journal of Neuroscience Methods 179:258-263. doi:10.1016/j.jneumeth.2009.02.001