Figure 1.

MEG Extension of the Tagamets-Horwitz (1998) large-scale neural model. (A) Locations in the ventral visual stream where sources are located for simulating MEG data. The 3-D Talairach coordinates have been projected to the nearest gray matter on the cortical surface within a window of 5 mm. The medial surface locations V1 and V4 are shaded in lighter color, pink whereas the lateral surface locations in inferior temporal (IT) and prefrontal cortex (PFC) in brighter red. (B) The basic Wilson-Cowan unit. E represents the excitatory population and / the inhibitory population in a local assembly such as a cortical column. Local synaptic activity is dominated by the local excitation and inhibition, while afferents account for the smallest proportion, as indicated by the synaptic weights shown. (C) A cortical area is modeled by a 9 × 9 set of basic units. The excitatory population is shown in bold lines above the inhibitory group, shown in lighter lines. Individual units in the excitatory and inhibitory populations within a group are connected as shown in (B). (D) The working memory circuit in the prefrontal area of the model. It is composed of different types of units, as identified in electrophysiological studies, and shown in (C). Each element of the circuit shown is a basic unit, as shown in (B). Inhibitory connections are affected by excitatory connections onto inhibitory units. These D2 units also are the source of feedback into earlier areas. Figures B–D are adapted with permission from (Tagamets and Horwitz, 1998).