A new approach for probing information flow during decision-making
November 11, 2013
Manipulating neural activity and measuring the effect on behavior is a key tool for understanding the function of a structure in the brain. Sometimes, experimenters will manipulate activity in two areas to gain insight into the flow of information through the brain. In a poster this year at SFN, Nuo Li, a postdoc in Karel Svoboda’s lab, took things a big step further by systematically suppressing the activity of 55 locations, each 1 mm wide, in the cortex of individual mice. He achieved this by using a pair of mirror galvos to move a stimulating beam to different places in the brain. In a given session, he could inactivate the parietal cortex on some trials, the somatosensory cortex on other trials and the anterior lateral motor cortex (ALM) on others still. This approach has a few advantages: first, by surveying the cortex broadly, he leaves open the possibility of identifying relevant areas that weren’t even on his radar. Second, the approach avoids a common pitfall of traditional stimulation experiments: in those experiments, the animal can notice a change in its performance and adapts its strategy. A signature of this nonstationary strategy is usually apparent in control trials. Here, the stimulation causes different effects depending on WHERE its targeted and WHEN in the trial it takes place, making it a challenge for the animal to respond with an altered strategy.
The group found that stimulating the ALM and the barrel cortex had the biggest effects on behavior. Barrel cortex inactivation mattered most when it was presented early in the trial, and ALM inactivation mattered most when it was late in the trial, consistent with the idea that information flows from the sensory area to the motor area over the course of decision formation. An interesting next step would be to uncover what aspect of the animal’s performance was disrupted by the inactivation. For example, interpreting the results would be aided by knowing whether the reduced performance on their task was driven by a change in sensitivity or a change in bias.