The effect of cortical and subcortical lesions on spontaneous expression of memory-encoded and emotionally infused information: Evidence for a role of the ventral stream.

Abstract

The ventral stream of language processing has been implicated in the spontaneous expression of memory-encoded and emotionally infused information. The present study investigated whether left hemispheric lesions in post-stroke right-handed aphasic patients may be selectively associated with specific language functions. Speech rate was assessed with two tasks, one based on autobiographical memory of an emotionally infused event (stroke story narration) and the other based on information that is visually available at the time of speech generation ("cookie theft" picture description). CT and/or MRI scans were obtained for each patient and lesions located in 16 regions of the left hemisphere were identified and coded. The total number of cortical and subcortical areas affected served as a measure of lesion extent. While mean speech rates were similar across conditions, there were different patterns of association between each index and specific lesion sites. Non-parametric quantile regression statistical models constructed to assess dependence of both speech rate indices on each lesion locus indicated that the speech rate in the stroke story had significant inverse associations with total number of lesioned areas, as well as lesions in the inferior frontal gyrus and the external/extreme capsule region. The cookie theft speech rate had significant inverse associations with total number of lesioned areas as well as lesion in the inferior frontal gyrus, but not with the external/extreme capsule region. In sum, integrity of the extreme/external capsule region appears to be important selectively for the Stroke Story task, supporting the hypothesis that the ventral stream plays a central role in spontaneous expression of memory-encoded and emotionally infused information.