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Anthony Norcia; Abnormal preparatory activity in amblyopia: Deficits beyond early visual cortex. Journal of Vision 2013;13(15):T35. doi: 10.1167/13.15.35.
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Predictable events in the environment allow us to prepare to process upcoming visual inputs (preparatory attention) and motor responses (motor planning). These preparatory signals originate in frontal and parietal areas that send outputs to motor planning areas and to posterior visual structures. Motivated by the fact that frontal and parietal cortex have long developmental sequences, we have been studying simple visual tasks that require control inputs from these areas in patients with a history of amblyopia. High-density EEG recordings, combined with source localization methods were used to study the spatio-temporal distribution of the two forms of preparatory activity. Motor planning and preparatory attention networks were studied in a simple go-no/go task in which the first stimulus (S1) provides a cue as to whether a response to a second stimulus presented 1 sec later might require a response (S2). On half of the trials, S1 indicated that a target would be presented at S2 with 50% probability. Trials of this type induce an expectation of the potential need to respond when S2 is presented. These trials generate a large negative going potential in areas associated with motor planning (the Contingent Negative Variation) as well as slow positive potentials in parietal and occipital cortex. While the magnitude of the motor planning potential was comparable between patients and controls, preparatory attention signals were selectively reduced in patients with amblyopia. The loss of top-down attentional inputs may contribute to previously observed behavioral deficits in amblyopia on tasks that require selective visual attention.
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