It is beyond our scope even to attempt a summary of this expanding literature. Instead, we will present some of the main dimensions of memory that this work has highlighted as having potential for understanding neural mechanisms. Procedural memory Both clinical and functional neuroimaging studies have supported distinct neural systems involved in “procedural” learning and memory, which differ from those regulating “declarative” memory. Procedural memory refers to retention of skills acquired by repeated

Inhibitors,research,lifescience,medical practice, while declarative memory refers to knowledge of content of previously experienced situations. As established by the case of HM and confirmed in functional neuroimaging studies, declarative memory involves the hippocampus and associated temporal and frontal cortices. Procedural memory is different, as has been Inhibitors,research,lifescience,medical established by psychologists long ago, in multiple respects. It is mostly unconscious and its learning depends more on rote repetition than on insight. Furthermore, once learned, it is retained after the passage of years. Examples are riding a bicycle, skiing, driving a car, and swimming. If trained in these skills at an early age, one can retain these skills Inhibitors,research,lifescience,medical and, while rusty after prolonged lack of practice, would show evidence of prior learning by rapid return to earlier skill levels. This learning takes place in regions outside the hippocampus, predominantly in cerebellum,

basal ganglia, and sensorimotor cortex. Declarative memory Declarative memory refers to specific autobiographical events that can be recounted by an individual. For example, a memory of your birthday when

you received a PI3K inhibitor bicycle as a gift. One is able to place the event in time and context. Further distinctions have been made within declarative memory, between episodic Inhibitors,research,lifescience,medical and semantic Inhibitors,research,lifescience,medical memory. Semantic memory is factual, whereas episodic memory contains representations of past experience that include sensory, perceptual, conceptual, and affective features.11 Episodic memory can fade rapidly and is subject to distortions.12 All forms of declarative memory appear to recruit medial temporal structures. However, there is evidence that prefrontal regions are involved in the encoding of new episodic memories. More recently an important distinction within episodic memory has been proposed—between recollection and familiarity.13 Recollection reflects the retrieval of information, whereas familiarity reflects the passing of a threshold where one recognizes a stimulus Cell press or event as having been experienced. There is much current research attempting to identify distinct neural systems related to recollection and familiarity.14 Note that another domain, working memory, is often discussed in functional neuroimaging studies. Although that construct described by Baddeley15 encompasses mnemonic processes as it relates to events immediately preceding the present, its emphasis is on the rapid replacement of information by new input entering our mental scratch pad.