Research Report 2010 - MDC

Structure of the GroupGroup LeaderDr. James Poulet*PostdocsJean-Sebastian Jouhanneau*Nevena Milenkovic*Birgit Voigt*James Poulet*start of the group : July 2009Neural Circuits and BehaviorRecent technical advances are allowing researchers to make high resolution recordings andmanipulations of brain activity even while animals are awake and behaving. These data areproviding remarkable insights into normal brain function. Of particular interest is the activity ofneurons in neocortex, as they are involved in conscious movement and sensory perception. Ourlab combines electrophysiological and optical neural recordings with genetically targetedmanipulations of neural activity in mice during trained behavior to investigate the link betweenneural activity, sensory perception and motor behavior.Brain states during behaviorThe very first recordings from the awake human brainby Hans Berger (1929) revealed distinct patterns of corticalactivity during different behavioral states.Different “brain states” were thought to reflect changesin the synchrony of cortical activity and be fundamentalto sensory perception, sensorimotor coordinationand learning. However, it was unknown how corticalsynchrony is reflected in the intracellular membranepotential (V m ) dynamics of behaving animals. With CarlPetersen (EPFL, Switzerland) we showed, using dualwhole-cell recordings from layer 2/3 primarysomatosensory mouse whisker barrel cortex, that theV m of nearby neurons is highly correlated while themouse is sitting still. However, when the mouse movesits whiskers, to sense the environment, an internallygenerated state change reduces the V m correlation(Figure 1).We went on to show that the rate of action potentialfiring was surprisingly low in layer 2/3 pyramidal neurons.Single action potentials were driven by a large,brief and specific excitatory input that was not presentin the V m of neighbouring cells. Action potential initiationoccurs with a higher signal-to-noise ratio duringwhisker movement as compared to quiet periods. Thechange in brain state therefore may increase the overallinformation coding capacity of the brain.We have gone on to investigate the neural mechanismsunderlying the change in brain state. So far we haveshown that the state change is not the result of sensoryfeedback as it persists even after cutting the primarysensory neurons that innervate the whisker pad (Figure2). We are presently investigating the role of the thalamusin regulating cortical state changes.Sensorimotor integration in the mouse forepawcortical regionOur lab will focus on the primary sensory and motorcortical areas associated with mouse forepaw. Neuronalactivity in cortical regions controlling limb movement isparticularly relevant in the emerging field of neuroprosthetics,where cortical activity from paralyzed patientsis used to drive robotic limbs.We will train mice to maketargeted reaching movements while recording andmanipulating cortical neural activity.Role of acetylcholine in cortical processing andbehaviorThe neocortex is densely innervated by axon fibers containingacetylcholine (ACh). Neurons containing AChhave received much attention, perhaps mainly becauseof their degradation in Alzheimer’s disease but also dueto their putative role in cognitive processing such as174 Function and Dysfunction of the Nervous System