Fig. 9. Behavior of a mature multisensory integrative neuron as function of AES cortex.

The figures show the activity of a SC neuron (in this case we used the SCN at position 47 in the network) in response to different inputs configurations, with AES active (left panels) and deactivated (right panels). In particular, here we present a neuron which has acquired both integrative capabilities during the development: cross-modal enhancement and multisensory depression. Dynamic Ranges (DRs) (upper figures). In all simulations the activity was assessed by stimulating the model with auditory (dash-dotted line), visual (dashed line) and multisensory (solid line) inputs at various intensities. The stimuli were presented in the center of the RF of the observed SC neuron. Note that with AES active, the simulated SC neuron shows multisensory enhancement in response to a cross-modal stimulation; if the AES is inhibited, the SC shows no multisensory integration, the unisensory responses are reduced by about 50% and the response to two cross-modal stimuli looks like the stronger unisensory one. Integration as a function of the position of two stimuli (lower panels). The figures show the response of the mature SC neuron to paired stimuli in different spatial configurations. Simulations are made by stimulating the model with an auditory (A) stimulus at the center of the RF of the observed SC neuron. The response elicited by this modality-specific stimulus (dashed thin lines) is then compared with those produced by coupling either a second auditory stimulus (dash-dotted lines) or a visual stimulus (solid lines) in different positions. The x axis displays the position of the second stimulus relative to the center of the RF. x = 0° means that both stimuli are at the center of the RF; increasing x means that the position of the second stimulus is increasingly farther from the RF. Results with AES active show: multisensory enhancement in the case of cross-modal stimulation inside the RF irrespective of the position of the two stimuli; no unisensory enhancement in case of a second within-modal stimulus inside the RF; multisensory and unisensory inhibition in the case of two stimuli far in space. In case of AES deactivated, the network shows the loss of multisensory enhancement in case of cross-modal stimulation inside the RF, and a slight inhibition in case of two stimuli of the same or different sensory modality far in space.