Performance on the N-Back Task Dissociates Dat Patients with Prefrontal Cortical Impairment from those without.

Abstract:
Twelve patients with dementia of Alzheimer's type, seven of whom showed impairment of prefrontal cortex according to data from SPECT imaging and a neurobehavioral examination, and five who did not, were administered a version of the n-back task, which is thought to involve executive functions of working memory. We observed an interaction between patient group and task complexity [F(1,10)=5.05; p<0.05], such that, while DAT patients who showed evidence of frontal impairment did not differ from those without frontal involvement in performance of the 1-back task (M=96+/-3% vs. M=88+/-6%), they demonstrated dramatic impairment, relative to non-frontal DAT patients, on the 2-back task (M=64+/-7% vs. M=83+/-8%; chance=50%). We argue that this finding provides further evidence of a role for prefrontal cortex in the integration of relational representations, as the 2-back task is distinguished from the 1-back task in that it requires the maintenance and integration of multiple relational position codes. This result also indicates that the executive control/working memory demands of the n-back task derive directly from the need to integrate relational representations.