Perirhinal cortex (PER) has a well established role in the familiarity-based recognition of individual items and objects. For example, animals and humans with perirhinal damage are unable to distinguish familiar from novel objects in recognition memory tasks. In the normal brain, perirhinal neurons respond to novelty and familiarity by increasing or decreasing firing rates. Recent work also implicates oscillatory activity in the low-beta and low-gamma frequency bands in sensory detection, perception, and recognition. Using optogenetic methods in a spontaneous object exploration (SOR) task, we altered recognition memory performance in rats. In the SOR task, normal rats preferentially explore novel images over familiar ones. We modulated exploratory behavior in this task by optically stimulating channelrhodopsin-expressing perirhinal neurons at various frequencies while rats looked at novel or familiar 2D images. Stimulation at 30–40 Hz during looking caused rats to treat a familiar image as if it were novel by increasing time looking at the image. Stimulation at 30–40 Hz was not effective in increasing exploration of novel images. Stimulation at 10–15 Hz caused animals to treat a novel image as familiar by decreasing time looking at the image, but did not affect looking times for images that were already familiar. We conclude that optical stimulation of PER at different frequencies can alter visual recognition memory bidirectionally.Unfortunately, given that rather fancy optogenetic methods were used to vary oscillatory activity in the perirhinal cortex, no human applications of this work are imminent.
Monday, October 19, 2015
A brain switch that can make the familiar seem new?
We all face the issue how to refresh and renew our energy and perspective after our brains have adapted, habituated, or densensitized to an ongoing interest or activity that lost its novelty. As I engage my long term interests in piano performance and studying how our minds work, I wish I could throw a "reset" switch in my brain that would let me approach the material as if it were new again. Ho et al. appear to have found such a switch, in the perirhinal cortex of rats, that regulates whether images are perceived as familiar or novel: