Anatomy of Nondeclarative Memory

Whereas declarative memory depends on the integrity of a limited number of brain regions, nondeclarative memory encompasses all other forms of memory mediated by all other brain regions. In this sense, nondeclarative memory may be described as more diffuse in its neural representation. Each specific form of nondeclarative memory, however, is closely linked to specific brain structures and regions.

Immediate memory stores appear to be located in posterior neocortical regions, the location reflecting the modality (auditory or visual) and material (verbal or nonverbal) of the briefly retained information. For immediate auditory memory, left and right temporal-parietal cortices, respectively, mediate auditory verbal and nonverbal material. For immediate visual memory, left and right occipitoparietal cortices, respectively, mediate immediate verbal and nonverbal material. Thus, a reduced ability to immediately recall aurally presented digit strings occurs in patients with left temporal-parietal lesions.

Working memory processes that support selective aspects of declarative memory have been linked to the dorsolateral frontal cortex and to basal ganglia and cerebellar areas that are directly or indirectly linked to the dorsolateral frontal cortex. The prevailing view is that there are discrete dorsolateral frontal areas that direct the rehearsal of the immediate memory stores. Thus, keeping a spatial location in mind may involve a right-frontal area that directs the maintenance of that information in a right parietal area, whereas keeping a word in mind may involve a left-frontal area that directs the maintenance of that information in a left temporal or parietal area.y Specific basal ganglia and cerebellar areas appear to support the working memory capacity of particular frontal regions.

Implicit memory processes appear to depend on the same brain regions that mediate performance in any given domain. By this view, implicit memory reflects adaptive plasticity within neural systems that occurs in the course of the support by those systems of particular forms of behavior. Thus, motor-skill learning has been linked to pyramidal, extrapyramidal, and cerebellar motor systems.^ Interestingly, perceptual and cognitive skill learning has also been linked to the same action systems, with some evidence indicating that they may reflect adjacent but separable frontostriatal and frontocerebellar circuits. Perceptual repetition priming has been linked to modality-specific neocortices (e.g., visual priming with visual cortex) y and conceptual repetition priming has been linked to polymodal linguistic neocortical regions in the left frontal and left temporoparietal areas. y

Classic conditioning has been well characterized as being dependent on the dentate and interpositus nuclei of the cerebellum in animals, and such conditioning depends on the same cerebellar structures in humans. y More complicated conditioning paradigms appear to require, in addition, medial-temporal regions. y

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