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The early components of visual evoked potentials are thought to reflect the activity of the visual sensory pathways at a subcortical level. Animal studies have provided evidence that the anatomical connections and related physiological mechanisms allow cortical modulation of the activity of the subcortical visual pathways. The present experiments investigated the modulation of early visual evoked potentials during a visual memory task in humans. The results revealed that three early components (P45, P75 and N100) were modulated by some cognitive processes related to memory. This memory-induced early modulation has been interpreted as reflecting the influence of descending afferent connections from the associative cortex to the subcortical visual relays. Such processes may assist the early selection of visual information as a function of the required task.

It has been demonstrated that the early components of visual evoked potential may be modulated by cognitive processes related to memory. This memory-induced modulation could reflect the influence of descending connections from the associative cortex to the subcortical relays. Considering the importance of the temporal cortex in memory processing the effect of unilateral temporal lesions on early evoked activity during a visual memory task was investigated. Results show that memory-induced modulation of three previously identified early components (P45, P75, and N100) is affected by both left and right temporal lobectomies. However, the right lobectomy mainly affects the P45 and P75 components, while the left temporal lobectomy affects the P75 and N100 components. The present data provide evidence that the activity in the subcortical visual relays is modulated by lateralized specific inputs from left and right temporal lobes. Early memory-induced modulation may therefore depend on some complex pathways involving both cortico-subcortical projections and interhemispheric connections.