Prefrontal cortical involvement in verbal encoding strategies

Abstract

The lateral prefrontal cortex is critical for the control and organization of information in working memory. In certain situations, effective reorganization can attenuate task difficulty, suggesting a dissociation between lateral prefrontal activity and basic memory demand. In a verbal working memory task, we investigated the enhancement of performance that occurs when incoming information can be reorganized into higher-level groups or chunks. In the fMRI scanner, volunteers heard and repeated a sequence of digits. Mathematically structured sequences, encouraging 'chunking', were compared with unstructured, random sequences. Though structured sequences were easier to remember, fMRI showed increased lateral prefrontal activation for these sequences. Specifically, both the dorsolateral and ventrolateral prefrontal cortices were activated preferentially for the structured sequences during encoding. When visual stimuli that can be chunked using spatial structure are used, similar results are observed. These results demonstrate that cognitively less demanding tasks may elicit greater lateral prefrontal recruitment. Thus, the lateral prefrontal cortex appears to play a general role in strategically recoding information from memory, in order to optimize performance.

Dorsolateral Prefrontal Cortex Promotes Long-Term Memory Formation through Its Role in Working Memory Organization

“…However, the RT on reorder trials did not differ as a function of subsequent memory performance, nor did it correlate with DLPFC subsequent memory effects. These findings are consistent with studies that have reported increased DLPFC activation in contrasts between conditions that were matched for difficulty (Cabeza et al, 2002) or during performance of the less difficult of two tasks (Braver and Bongiolatti, 2002;Bor et al, 2004). Additionally, in the extant encoding literature, four of the five encoding studies that reported significant accuracy differences between encoding tasks do not report DLPFC subsequent memory effects in either the more difficult or the relatively easier condition (Chee et al, 2003;Clark and Wagner, 2003;Reynolds et al, 2004;de Zubicaray et al, 2005) (but see Baker et al, 2001).…”

“…DLPFC activation has also been reported in studies investigating "chunking," which involves processing of relationships to build higher-level groupings among items that are active in WM (Bor et al, 2004). Reasoning tasks, which entail extraction and integration of relationships among verbal propositions (Bunge et al, 2005), mathematical operations , or complex visual objects (Christoff et al, 2001;Kroger et al, 2002) active in WM have also been shown to activate the DLPFC.…”

Functional Coupling of Human Prefrontal and Premotor Areas during Cognitive Manipulation

“…Referencing to LTM may have induced the VLPFC activity, which was observed during both recoding and manipulation processes. VLPFC activity was reported during a knowledge-based chunking task, which required subjects to retrieve task-relevant information from LTM (Bor et al, 2004). Similar VLPFC activity was observed during stimulus-response linkage tasks (Petrides, 2002;Prince et al, 2005;Hanakawa et al, 2006).…”

KIBRA and CLSTN2 polymorphisms exert interactive effects on human episodic memory

“…In addition, the tasks used varied not only in their associative demands, but also required different processing strategies. Whereas item memory seems to depend on MTL structures (Eichenbaum et al, 2007;Squire, Stark, & Clark, 2004), story processing requires the strategic manipulation and organization of information, which largely depends on the prefrontal cortex (Addis & McAndrews, 2006;Bor, Cumming, Scott, & Owen, 2004;Fletcher, Shallice, & Dolan, 2000). Therefore, the results may reflect differences in task strategy as opposed to differences in associative task demands.…”