Spike transfer and sensitivity control in thalamic and cortical `hybrid networks'

Thierry Bal,1 Gwendal Le Masson,2 Damien Debay,1 Sylvie Renaud,3 M. Badoual,1 Y. Shu,4 A. Hasenstaub,4 and David McCormick4

2Institute F. Magendie
3University Bordeaux
4Yale University

The response of thalamic and cortical neurons to individual synaptic inputs is potentially influenced by local synaptic interactions and by the state of the network in a continuum from sleep to waking. We examine these properties using new hybrid technology (Le Masson et al., 2002) in which a biological neuron is connected to silicon and computer-based simulated neurons through artificial synaptic connections. Individual membrane currents of the simulated and biological neurons and the properties of their synaptic connections can be selectively and quantitatively controlled throughout their dynamic range.

The thalamus is the major gateway for the flow of sensory information to the cerebral cortex. In early stages of sleep, when sensory perception drops, this structure is the source of robust network synchronized oscillations in the 6 to 14 Hz frequency range (spindle waves). We examine the role of these thalamic oscillations in the gating of synaptic inputs. We show that feedback inhibition from cells of the thalamic reticular nucleus controls spike transfer in thalamocortical cells in a state-dependant manner.

Neurons in the cerebral cortex are under a constant state of bombardment by synaptic potentials. We have used a computational model (Destexhe et al., 2001, Neurosci. 107:13) that mimics the synaptic bombardment of thousand of cells. This 'noise' injected in pyramidal cells reproduces the spontaneous activity recorded in the biological network in vivo or in vitro. Using the hybrid system, we can the test the impact of background synaptic activity on the probability of spike response to individual synaptic inputs.