Modeling of cortico-pulvino-cortical in cats

Master 1 dissertation

The pulvinar, the largest thalamic nucleus in mammals, has connections throughout the cortical architecture of visual areas. It is reciprocally connected to visual areas 17 and 21a in cats and allows the transfer of information from the thalamus to the cortex. This type of neuronal transmission is defined as the transthalamic pathway. Little is known about the role of the transthalamic pathway in the temporal coordination of spiking activity between visual cortical areas. To address this question, we investigated the spike synchronization of single units (SU) in areas 17 and 21a of anesthetized cats when pulvinar was inactivated (100 mM of GABA, 1 μl). SU responses to drifting gratings presented at different contrast levels were recorded simultaneously in the two cortical areas. Only one of the four simultaneous penetrations had an increase of synchronous firing rate at higher visual contrast levels, showing a contrast response function (CRF) profile. During pulvinar inactivation, the dynamic range of the CRF (Rmax) decreased and increased in areas 17 and 21a, respectively. To explain such synchronous modulation, a network representing the three areas of interest (areas 17 and 21a, and the pulvinar) was modelled. Each area composed of 10000 spiking neurons, was simulated to obtain a balanced state between excitatory and inhibitory inputs. The theoretical neural network mimicked the simultaneous modulation of the Rmax when the weight of connectivity between areas was asymmetric. Such results were obtained when the transthalamic pathway has a strong feedforward component. Our theoretical findings suggest that the asymmetry of connectivity between the different regions is crucial to the transmission and regulation of visual information across the visual cortex.