Prefrontal regions supporting spontaneous and directed application of verbal learning strategies: Evidence from PET

Abstract

The prefrontal cortex has been implicated in strategic memory processes, including the ability to use semantic organizational strategies to facilitate episodic learning. An important feature of these strategies is the way they are applied in novel or ambiguous situations-failure to initiate effective strategies spontaneously in unstructured settings is a central cognitive deficit in patients with frontal lobe disorders. The current study examined strategic memory with PET and a verbal encoding paradigm that manipulated semantic organization in three encoding conditions: spontaneous, directed and unrelated. During the spontaneous condition, subjects heard 24 words that were related in four categories but presented in mixed order, and they were not informed of this structure beforehand. Any semantic reorganization was, therefore, initiated spontaneously by the subject. In the directed condition, subjects were given a different list of 24 related words and explicitly instructed to notice relationships and mentally group related words together to improve memory. The unrelated list consisted of 24 unrelated words. Behavioural measures included semantic clustering, which assessed active regrouping of words into semantic categories during free recall. In graded PET contrasts (directed > spontaneous > unrelated), two distinct activations were found in left inferior prefrontal cortex (inferior frontal gyrus) and left dorsolateral prefrontal cortex (middle frontal gyrus), corresponding to levels of semantic clustering observed in the behavioural data. Additional covariate analyses in the first spontaneous condition indicated that blood flow in orbitofrontal cortex (OFC) was strongly correlated with semantic clustering scores during immediate free recall. Thus, blood flow in OFC during encoding predicted which subjects would spontaneously initiate effective strategies during free recall. Our findings indicate that OFC performs an important, and previously unappreciated, role in strategic memory by supporting the early mobilization of effective behavioural strategies in novel or ambiguous situations. Once initiated, lateral regions of left prefrontal cortex control verbal semantic organization.

Improvement in memory and static balance with abstinence in alcoholic men and women: Selective relations with change in brain structure

“…Our measure of lateral ventricular volume might be taken as an approximation of the integrity of adjacent structures and regions invoked in the WMS-R battery (cf, Symonds et al, 1999). These include frontal lobe systems, used for strategic executive function, such as self-cueing and semantic organization (Incisa della Rocchetta and Milner, 1993;Fletcher et al, 1998;Savage et al, 2001), and medial temporal lobe structures used for nonstrategic declarative memory (Zola-Morgan and Squire, 1992;Corkin et al, 1997). Importantly, associations were not present between change in memory and change in the fourth ventricle, a CSF-filled space adjacent to the cerebellum.…”

“…Cognitive functions most likely to recover, patient characteristics most likely to predict recovery, and time course for such recovery have important implications for treatment (Goldman, 1995;Nixon et al, 1998;Bates et al, 2002). When memory tasks require active strategies for encoding, semantic organization, and retrieval of learned material, they probably draw on frontal executive systems (e.g., Incisa della Rocchetta and Milner, 1993;Fletcher et al, 1998;Savage et al, 2001) and medial temporal systems required for formation of new memories (for review see, Gabrieli, 1998). Deficits in such strategic memory tasks can occur with chronic alcoholism (Brandt et al, 1983;Rourke and Grant, 1999;Munro et al, 2000;Sullivan et al, 2000d;Sullivan et al, 2002;Fama et al, 2004); (for reviews see, Parsons, 1987b;Riege, 1987;Oscar-Berman and Marinkovic, 2003) but can also recover with abstinence (Parsons, 1987a;Fein et al, 1990;Fein et al, 2006).…”

Evidence of an amnesia-like cued-recall memory impairment in nondementing idiopathic Parkinson's disease

“…Evidence of poor performance of these executive processes (for a review see Dirnberger & Jahanshahi, 2013) Q4 and functional brain imaging evidence of reduced (medial) prefrontal activation and elevated false alarm rate during a yes/no item recognition memory task in PD (e.g., Segura, et al, 2012) has led to proposals that the prefrontal dependent executive deficits underlie the breakdown of recall, which often depends on effortful and organized encoding and retrieval processes. The impaired executive control processes normally underlie the organization of material at encoding and the search for better cues at retrieval as well as retrieval-related activities, such as response monitoring and decision-making (e.g., Gabrieli, et al, 1996;Mayes & Daum, 1996;Savage, et al, 2001).…”

Theoretically derived CVLT subtypes in HIV-1 infection: Internal and external validation

“…An ineffective learning style, reflected by poor use of semantic clustering, an elevated recency effect (passive recall of items at the end of the list), and inconsistent recall of list items, has been reported with individuals with HIV-1 infection Peavy et al, 1994). Moreover, organizational strategies that facilitate learning have been linked to prefrontal cortex (Savage et al, 2001;Stuss et al, 1994), a region that is vulnerable to the effects of HIV-1. Thus, how well an individual is able to learn may depend on the functional integrity of prefrontal brain systems.…”