Redefining implicit and explicit memory: The functional neuroanatomy of priming, remembering, and control of retrieval

Abstract

We used event-related functional MRI to study awareness of prior episodes during memory retrieval and its relationship to the intention to retrieve memories. Participants completed cues with words from a prior list (intentional test) or with the first words that came to mind (incidental test). During both tests, explicit memory was separated from priming in the absence of explicit memory. Priming was associated with hemodynamic decreases in left fusiform gyrus and bilateral frontal and occipital brain regions; explicit memory was associated with bilateral parietal and temporal and left frontal increases. Retrieval intention did not change these patterns but was associated with activity in right prefrontal cortex. Our results provide firm evidence that implicit and explicit memory have distinct functional neuroanatomies, and that strategic control of retrieval engages brain structures distinct from those involved in both implicit and explicit memory. They have critical implications for theories of memory and consciousness, which often equate consciousness with control.

Suppressing Unwanted Memories Reduces Their Unconscious Influence via Targeted Cortical Inhibition

“…Neural priming has been observed with fMRI in humans (23)(24)(25), and with single unit recording in nonhuman primates (35). Strikingly, neural priming occurs even when people do not report conscious memory for previous presentations of a stimulus (25).…”

“…marker of perceptual memory is neural priming, or reduced brain activity in areas that process a stimulus, when the stimulus is repeated (23)(24)(25). Neural priming has been observed with fMRI in humans (23)(24)(25), and with single unit recording in nonhuman primates (35).…”

“…Neural priming has been observed with fMRI in humans (23)(24)(25), and with single unit recording in nonhuman primates (35). Strikingly, neural priming occurs even when people do not report conscious memory for previous presentations of a stimulus (25). In our perception task, we observed robust neural priming for studied items (that is, activation in response to think, no-think, or baseline items was less than for new items) in ventral visual stream areas involved in object perception (P FWE < 0.05; Fig.…”

“…In general, viewing a stimulus makes it easier to identify the same stimulus later on, a form of repetition priming (21)(22)(23)(24). Although this speeded perception may be followed by conscious memory for the repeated stimulus, the repetition priming benefit does not depend on such recognition, occurring undiminished in patients with organic amnesia (8) and in neurologically normal subjects with no conscious memory of the repetition (25,26). Thus, we expected participants to identify the studied objects more quickly than the new (unprimed) objects, and we interpret this repetition benefit to reflect the unintended influence of memory on perception.…”

Alzheimer's disease and implicit memory

“…however, each process has separate mechanisms 26,30,31 . Priming is influenced by frontal cortex, which may reflect its attentional demands [32][33][34] and procedural memory is influenced by the striatum, sensorimotor cortex and cerebellum 30,35,36 , which may reproduce its motor skills. explicit memory impairment is one of the earliest AD symptoms, and its loss characterizes all the stages of AD 37 .…”