Figure 1. Factors that modulate visual cortical plasticity.

(a) Left, a visual stimulus is initially registered by a fast feedforward wave of activity that activates feature selective neurons in the many areas of the visual cortex. Right, neurons in the frontal cortex engage in a competition to select a behavioral response, and the neurons that win the competition feed attentional signals back to the visual cortex. Neuromodulatory systems, including acetylcholine (green) and dopamine (purple), modulate the activity as well as the plasticity of sensory representations. (b) Contour grouping task where monkeys have to trace a target curve (T) that is connected to a fixation point (FP). A red circle at the end of this curve is the target for an eye movement (Figure 1b). The animals have to ignore a distractor curve (D). The two stimuli differ so that the RFs of neurons in areas V1 and FEF are either on the target curve (upper panel) or on the distractor curve (lower panel). (c) Neurons in the frontal cortex (area FEF) and the visual cortex (area V1) enhance their response when the target curve falls in their receptive field. Note that this attentional modulation comes at a delay (striped bar), while the initial neuronal responses do not discriminate between the relevant and irrelevant curve (black bar). Modified from Khayat et al. [70].