Psychotherapy and Neuroscience

Explicit (Declarative) Memory & the MTL

Explicit and declarative memory needs the support of and is dependent on a functional medial temporal lobe MTL (Squire, 1992). Loss of hippocampal viability causes deficits in retrievable recognition and in recollection of human faces, identification of voices, spoken words, and in acquiring definitions. Its loss also impairs the acquisition of allocentric information, i.e. acquiring associational relationships between objects with their locations and words in their temporal positions (Mayes, Holdstock, Isaac, Montaldi, Grigor, Gummer et al., 2004; Yonelinas, Kroll, Quamme, Lazzara, Sauve, Widaman et al., 2002). Destruction to the hippocampal system impairs delayed recall, recognition ability, declarative knowledge and awareness of repeating sequences (Squire, Schmolck, & Stark, 2001; Stefanacci, Buffalo, Schmolck, & Squire, 2000). Patients with amnesia syndrome and damage to the MTL have spared implicit-nondeclarative memory but lose their ability for spontaneous recall of recently learned facts or interpersonal experiences as noted in the patient, H.M., earlier.

Neuroimaging findings also support the essential role of the hippocampal region in facilitating semantic processing (Heckers, Weiss, Alpert, & Schacter, 2002; Wagner, Schacter, Rotte, Koutstaal, Maril, Dale et al., 1998) and intentional learning (Reber, Gitelman, Parrish, & Mesulam, 2003). Regional cerebral blood flow (rCBF) activations in the left mid-anterior hippocampus along with the parahippocampal gyrus, amygdala and medial prefrontal cortex facilitate the retrieval of recent and personally meaningful autobiographical memory (Maguire & Frith, 2003; Maguire & Mummery, 1999; Piefke, Weiss, Zilles, Markowitsch, & Fink, 2003). The anterior hippocampus with the amygdala facilitates the retrieval of personally relevant emotional episodes (Maguire & Frith, 2003) involving emotions of happiness, anger, or fear in interaction with cortical regions (Damasio, Grabowski, Bechara, Damasio, Ponto, Parvizi, & Hichwa, 2000) like the medial (Vogt, Berger, & Derbyshire, 2003) and anterior (Macrae, Moran, Heatherton, Banfield, & Kelley, 2004) prefrontal cortices. The hippocampus in coordination with other brain regions facilitates explicit episodic autobiographical memory.

The hippocampus also has a role in mediating the retrieval of conjunctive information of episodic memory. It binds a variety of sensory, affective, cognitive and behavioral elements of experiences associated with an event into a cohesive episode (Davachi, 2004; Jackson & Schacter, 2004). The hippocampal region, as such binds object, temporal, and contextual information to create a retrievable coherent and sequential internal representation of an episode’s what, where, and when (Ergorul & Eichenbaum, 2004; Fortin, Agster, & Eichnbaum, 2002). Organizing neural information in this way enhances retrieval of long term memory’s formation, storage, and retrieval.

The ability for performing relational memory processing about the nature of relationships between items also depends critically on an intact hippocampus. The hippocampus mediates the comparisons and relations between different individual representations with one another along with their relationship with coexisting memory structures and organization. As novel items and new information are encountered, the hippocampus processes how they relate to personally meaningful and existing schema (Eichenbaum & Cohen, 2001). Hippocampal activity and relational processing also correlates with the enhanced ability for later successful retrieval (Davachi & Wagner, 2002). It is through this capability that the hippocampus mediates flexible declarative (explicit) learning and retrievable memory. It makes “a unique contribution that allows lessons from the past to be applied to the future” (Preston, Shrager, Dudukovic, & Gabrieli, 2004, p. 150). Successfully completed psychotherapy noted later on may also mediate these processes as well.


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