Frontiers in Psychology (Apr 2014)
White matter pathways critical for language are also critical for resolving proactive interference in working memory
Abstract
Background White matter pathways connecting brain regions involved in language processing in the left prefrontal (PFC) and temporal cortices have been found to play a critical role in language comprehension (Turken and Dronkers, 2011). Among the frontal brain regions associated with language processing, the left inferior frontal gyrus (lIFG) has also been strongly associated with resolving proactive interference in working memory (Jonides and Nee, 2006). Here we investigated whether the white matter pathways connecting the lIFG to the left temporal lobe found to be important in language comprehension were also critical for resolving proactive interference in working memory. Methods We tested 4 patients with left PFC damage involving the lIFG, 5 with left temporal damage and 6 age-matched controls. Critically, 2 left PFC patients and 1 left temporal patient had lesions involving a complete disconnection between the lIFG and the left temporal cortex and the remaining patients had partial disconnection only. Performance was assessed using the Recent Probes test (Monsell, 1978): 4 visually-presented letters are followed by a probe: one central letter. The task was to decide whether or not the probe was part of the immediately preceding set of letters. Whether or not the probe was also part of the previous trial and elicited a positive or negative response was then manipulated and created recent negative (RN) and recent positive trials, respectively. RN trials generated interference in trial n compared to non-recent negative (NN) trials. Behavioral results were reported using error rates as the dependent variable. Results When the groups were separated based on which cortical lobe was damaged, there was a significant main interference effect (F(1,12)=24.94, p <.001), where RN trials were associated with worse performance than NN trials, and a main effect of group (F(2,12)=4.65, p <.05), where performance was worse for patients than for controls, but there was no interaction between the size of the interference effect and group (F(2,12)=1.86, p =.198). Critically, when the left temporal patient who had a total disconnection with the left IFG was included in the left PFC group, there were still main effects of interference and group but there was also a significant interaction between the size of the interference effect and group (F(2,12)=5.31, p<.05), the interference effect was larger for patients having left IFG lesions and/or a total disconnection between the lIFG and the temporal lobe than for controls or for temporal patients without total disconnection (see table 1). Conclusions Our results are in agreement with the idea that the lIFG plays a critical role in resolving proactive interference in working memory (Jonides and Nee, 2006). However, our results also suggest that the lIFG may not be the only critical structure needed for such a mechanism. Indeed, similarly as in language processing, white matter pathways connecting the lIFG to the left temporal lobe seem to be critical for resolving proactive interference in working memory. This further suggests that a common underlying mechanism may be involved in both cognitive functions.
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