Inhibition in verbal working memory revealed by brain activation

Abstract

There are many occasions in which humans and other animals must inhibit the production of some behavior or inhibit the processing of some internal representation. Success in inhibitory processing under normal circumstances can be revealed by the fact that certain brain pathologies render inhibitory processing ineffective. These pathologies often have been associated with damage to frontal cortex, including lateral and inferior aspects. We provide behavioral evidence of a verbal working memory task that, by hypothesis, engaged inhibitory processing, and we show (by using positron emission tomograpny) that the inhibitory processing is associated with a lateral portion of the left prefrontal cortex. The task in which subjects engaged was item-recognition: Four target letters were presented for storage followed, after a brief interval, by a probe letter that could match a target letter or not. On some trials, when the probe did not match a target letter and therefore required a "no" response, the probe had matched a target letter of the previous trial, so on these trials a "yes" response was prepotent and had to be inhibited, by hypothesis. Compared with a condition in which no prepotent response was created, this condition yielded brain activation in left inferior frontal gyrus, in the region of Brodmann's area 45.

Figure 1

Images reflecting the activations in three subtractions. Each row presents left lateral, superior, and right lateral views of the brain, with t statistics of activations at or within 15 mm of the surface superimposed in color on a gray MRI of a single subject (not one from this study). Red represents the largest ± value, followed by yellow, green, and blue. Shown are all activations that passed a criterion of P < 0.05 uncorrected for multiple comparisons (although statistical analysis corrected for multiple comparisons in revealing the sites of activations that are listed in Table 2). The top row depicts the sites of activation subtracting the Low from the High Recency condition; the second row depicts the sites from the subtraction of the Low Memory from the High Recency condition; and the bottom row shows the subtraction of the Low Memory from the Low Recency condition.