Cosyne 2008 Workshops
March 3-4, 2008
Snow Bird, Utah
Authors
David A. McCormick, Bilal Haider, Andrea Hasenstaub, Yousheng Shu, Alvaro Duque Dept. Neurobiology, Kavli Institute for Neuroscience, Yale University School of Medicine
Talk Title
Recurrent cortical networks and the control of neuronal responsiveness.
Talk Abstract
Cortical networks are characterized by strong local and long distance recurrent excitatory connections that are controlled by local inhibitory systems. We have investigated the properties of these recurrent networks through both in vivo and in vitro techniques in prefrontal and visual cortical regions. In anesthetized animals, or cortical slices in vitro, cortical networks generate periods of persistent activity (Up states) interspersed with periods of silence (Down states). Intracellularly these Up states are characterized by strong and balanced barrages of excitatory and inhibitory synaptic potentials mediated by activity of neighboring cortical neurons. Interestingly, the transitions between active (Up) and inactive (Down) states occur rapidly, within approximately 50 msec, and occur first in layer 5, followed by a rapid propagation to other layers. Examination of excitatory versus inhibitory postsynaptic potentials during the period of persistent activity revealed that the inhibitory network dominated higher frequency (> 20 Hz) activity. Extracellular single unit recordings in vivo reveal two groups of cells, differentiated by the properties of their action potentials. Fast spiking putative interneurons exhibited strong modulation in their firing rate in conjunction with the generation of gamma-frequency oscillations in the local field potential. Regular spiking, presumed pyramidal, cells were also modulated in their firing rate, but much more weakly. These results suggest that inhibitory networks are critically involved in the generation of higher frequency oscillations in cortical networks. Indeed, the intracellular injection on mixed inhibitory and excitatory conductances revealed that action potentials are often initiated in response to the rapid withdrawal of inhibition. Our results indicate that the precise interaction of local inhibitory and excitatory cortical networks determine the timing and gain of cortical responses. Understanding cortical networks will ultimately require the dissection of cortical networks by neuronal cell type.
