Fig. 2.

A neural network model of a local cortical circuit and TMS. The model represents a hypercolumn in early visual cortex, showing an orientation tuning function. The model consists of multiple neurons, each of which exhibits an orientation preference in a range of −90 to 90 degrees. The neurons are connected by excitatory and inhibitory synapses unless otherwise stated. Synaptic connections have a Mexican-hat-like structure (gray dashed line). The excitatory synapses exhibit cosine-type modulation depending upon differences in orientation preferences, and inhibitory synapses are uniformly distributed. Thus, neurons with similar orientation preferences excite each other, whereas all the neurons inhibit each other. Afferent input encodes stimulus orientation by firing rate. TMS is modeled as an excitatory current input with a short duration. Since the spatial extent of the TMS-induced magnetic field is significantly larger than the spatial scale of the cortical hypercolumn, TMS is assumed to stimulate all cortical neurons uniformly