Ventrolateral and dorsomedial frontal cortex lesions impair mnemonic context retrieval

Abstract

The prefrontal cortex appears to contribute to the mnemonic retrieval of the context within which stimuli are experienced, but only under certain conditions that remain to be clarified. Patients with lesions to the frontal cortex, the temporal lobe and neurologically intact individuals were tested for context memory retrieval when verbal stimuli (words) had been experienced across multiple (unstable context condition) or unique (stable context condition) contexts; basic recognition memory of these words-in-contexts was also tested. Patients with lesions to the right ventrolateral prefrontal cortex (VLPFC) were impaired on context retrieval only when the words had been seen in multiple contexts, demonstrating that this prefrontal region is critical for active retrieval processing necessary to disambiguate memory items embedded across multiple contexts. Patients with lesions to the left dorsomedial prefrontal region were impaired on both context retrieval conditions, regardless of the stability of the stimulus-to-context associations. Conversely, prefrontal lesions sparing the ventrolateral and dorsomedial regions did not impair context retrieval. Only patients with temporal lobe excisions were impaired on basic recognition memory. The results demonstrate a basic contribution of the left dorsomedial frontal region to mnemonic context retrieval, with the VLPFC engaged, selectively, when contextual relations are unstable and require disambiguation.

Keywords: context retrieval; dorsomedial frontal cortex; hippocampus; memory retrieval; prefrontal cortex; ventrolateral prefrontal cortex.

Figure 1.

(a) Schematic diagram of the testing procedure of the recognition memory condition, (b) the stable context retrieval condition and (c) unstable context retrieval condition. Note that the size of the screen for the encoding and retrieval phases was exactly the same in the experiment. However, in order to make the words legible in the illustration, the screen is enlarged and the question is removed in the retrieval phase. ISI, interstimulus interval.

Figure 2.

Graph showing the mean performance of each group across the three memory retrieval conditions. Error bars represent the standard error. *p < 0.05.

Figure 3.

Graph showing the mean performance on the three memory retrieval conditions of the four frontal groups: patients with lesions (i) including the left ventrolateral prefrontal cortex (left VLPFC), (ii) including the right VLPFC, (iii) including the left dorsomedial frontal cortex (left DMFC), (iv) sparing both the VLPFC and left DMFC (other FC) and of normal control subjects (HC). Error bars represent the standard error.