Functional anatomical studies of explicit and implicit memory retrieval tasks

Abstract

Across three experiments, PET scans were obtained while subjects performed different word-stem completion and FIXATION control tasks designed to study the functional anatomy of memory retrieval. During each of three different word-stem completion scans, word-stem cues were visually presented in uppercase letters. The RECALL task required explicit retrieval of study words presented prior to the PET scan. The PRIMING task addressed the implicit effects of the prior study words without requiring intentional recall. The BASELINE task encouraged retrieval of information from a general knowledge store. Across experiments, the similarity between study words and word stems was manipulated by presenting prescan study words in either uppercase letters identical to the stems, in lowercase letters, or auditorily. The PRIMING task was not studied with auditory presentation. Many activations were consistent across experiments. The BASELINE task activated several regions in response to the reading and verbal- response demands of the task (visual, motor, and premotor cortices, cerebellum), as well as a left prefrontal region. The RECALL task additionally activated regions in anterior right prefrontal cortex. Bilateral occipitotemporal regions showed blood flow reductions during the PRIMING task as compared to the BASELINE task. Activation in the right hippocampal/parahippocampal region was observed only in one experiment, and no experiment showed activation in the left medial temporal lobe. These experiments suggest that areas of frontal cortex play a role in explicit recall and that an effect of priming may be to require less activation of perceptual regions for the processing of recently presented information.

The cognitive neuroscience of memory: perspectives from neuroimaging research

“…Instead, hippocampal activation may be related to the level or type of recall in a particular situation: some aspect of the actual recollection of a past event, as opposed to the e¡ort involved in attempting to remember the event. These observations are consistent with Buckner et al's (1995) failure to observe hippocampal activation in di¡erent modality and di¡erent case conditions. Although subjects were trying to recall study list words in both conditions, the way in which they remembered those words may have di¡ered from the way in which they remembered words in the same case condition.…”

The neural basis of the bilateral distribution advantage

“…Name matching also elicited an activation in right frontopolar cortex. This area has often been reported to support retrieval processes (Buckner et al 1995(Buckner et al , 1998Squire et al 1992). Since letter name matching is distinct from letter shape matching in that the letter identity has to be accessed, it may be that right frontopolar cortex supports retrieval of letter identity from semantic memory in name matching.…”

An Event-Related fMRI Investigation of Implicit Semantic Priming

“…Results of a series of studies involving both perceptual and conceptual priming have shown that the previous presentation of a stimulus results in decreases in activation in neural areas related to the task requirements (for reviews, see Buckner et al, 1995;Buckner et al, 1998;Raichle et al, 1994). These findings emerge in different modalities (Buckner, Koutstaal, Schacter, & Rosen, 2000), with single or repeated presentations (Demb et al, 1995), with items that are perceptually different exemplar across repetitions (Koutstaal et al, 2001), and appear to be both task and process specific (Wagner, Koutstaal, Maril, Schacter, & Buckner, 2000;Demb et al, 1995).…”