June 2 2017 – INMED
Meeting at 10 am for the students of the ICN PhD program
“Geometry and State-dependence of population codes in the rat auditory cortex”
During the last few years, it has become apparent that the way information is represented in sensory cortex is strongly dependent on ‘brain state’. Brain states represent modes of global coordination in brain activity, and are modulated by the behavioral and neuro-modulatory state of the animal. A salient axis of variation in brain-state is the Activation/Inactivation continuum, which measures the extent to which local populations display (Inactive/Synchronized state) or not (Active/Desynchronized state) slow, global fluctuations in activity. The degree of Activation/Inactivation in the cortex strongly varies both within wakefulness, sleep, and anesthesia. I will describe how changes in cortical Activation shape the representation of sounds by populations of neurons in the rat auditory cortex during Urethane anesthesia, focusing on the coding of level intensity differences across the two ears. Using princpial component analysis, we characterize the geometry of representations at the population level, showing how the signal subspace (related to the tuning curves of the neurons) and noise subspace (related to their trial-to-trial variability) change as a function of brain-state. Our results suggest that the Activation/Inactivation continuum is characterized by a shift from a population code based on intensity (different stimuli lead to overall different numbers of action potentials fired by the population) to a population code based on identity (different stimuli result in approximately similar overall number of spikes, but fired by different subsets of neurons).