Figure 6. A computational model describing changes in extrastriate visual responses produced by signals from FEF delay neurons.

(a) Model architecture depicting extrastriate modulation as derived from pools of persistently active, delay neurons in the FEF (brown circles), which are organized topography across visual space (top row). Persistent activity is presumed to emerge from recurrent excitatory connections (white) within each pool³⁴,⁷⁰, as well as competitive inhibitory connections (black) between neighbouring pools. Persistent activity is sent via excitatory projections to extrastriate areas such as V4 and MT (bottom row), where neurons project feed-forward inputs to the FEF. (b) Population response of model extrastriate units to a visual stimulus presented at a location highlighted by the white line (see Methods for details) in the absence of a memory signal (see Methods for details). (c) When remembering a location (grey line), FEF maintains elevated activity (top panel). Consistent with the experimental observations, the delay signal does not alter baseline activity in extrastriate cortex (bottom panel, delay period). However, on presentation of a visual probe at the same location as in b the FEF delay signal modulates the response to the visual stimulus when probed during the delay period, resulting in a shift of the population response towards the centre of the delay signal, and an increase in gain. (d) Example RF of model extrastriate unit. The blue curve depicts the model RF when measured in the absence of a delay signal. The red curve indicates the RF of the same model neuron when measured in the presence of a delay signal that maintains the location highlighted by the arrow.