December 31, 2006

Conscious and nonconscious memory related brain activity

Are conscious and nonconscious processes supported by overlapping brain regions? In a recent study, Slotnick and Schacter investigated whether activity, related to visual memory, in early visual regions (BA17 and BA18) is reflective of nonconscious processing. The results of their study suggest that early visual regions (BA17, BA18) are associated with nonconcsious memory, while late visual regions (BA19, BA37) are associated with conscious memory. Click through for abstract. Hubmed.

The nature of memory related activity in early visual areas.
Slotnick SD, Schacter DL
Neuropsychologia. 2006; 44(14): 2874-86

Memory for visual items can evoke activity in visual processing regions, which is typically assumed to reflect conscious remembering. However, based on previous findings, we hypothesized that such activity in early visual areas (BA17, BA18) may reflect priming, a form of nonconscious memory. We tested this hypothesis in two fMRI experiments with similar stimulus protocols, but explicit or implicit task instructions. During initial runs, abstract shapes were presented to either side of fixation, filled with parallel lines of random orientation and color. In subsequent runs, old and new shapes (plus related shapes in Experiment 2) were presented at fixation. In Experiment 1, participants were instructed to remember each shape and its spatial location during initial runs; during subsequent runs they classified each shape as old and on the “left”, old and on the “right”, or “new”. A right fusiform gyrus region (BA18) and a left lingual gyrus region (BA18) were preferentially associated with shapes previously presented on the left and right, respectively. In support of our hypothesis, this early visual area activity was independent of response accuracy for spatial location. In Experiment 2, for each shape, participants identified parallel line orientation relative to horizontal. Consistent with our hypothesis, specific neural activity was observed in early visual regions (BA17, BA18, extending into BA19), with old activity greater than related and new activity (likely reflecting priming). The results of these experiments provide convergent evidence that memory related early visual area activity (BA17, BA18) can reflect nonconscious processing.

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