Fig. 2. SC responses and targeting synaptic strengths in the newborn.

Responses of a simulated immature SC neuron to different spatial configurations of modality-specific and cross-modal stimuli (a, b). The dark grey circles on the left represent qualitatively the visual RF of a SC neuron, while the light grey circles represent its auditory RF. We used this schematic representation to replicate that adopted by Stein and colleagues (see for example (Wallace and Stein 1997)) to facilitate the comparison between the simulated results and the data present in literature. The neuron is incapable of integrating its two cross-modal inputs and has responses equivalent to those of the stronger of the two. Figures 2.c and 2.d report the strengths of the incoming excitatory synapses that this SC immature neuron receives from the four unisensory input regions; in figures the x-axis represent the position of the pre-synaptic unisensory neurons, while the y-axis reports the synaptic strength of the connections. In this phase, the SC targeting synapses from AES subregions (panels c) are ineffective; on the contrary, the projections from non-AES input areas are diffuse and weak (panels d). Finally, in the neonatal condition, the SC doesn’t present any lateral interaction (fig. 2.e).