Illustrations-Multiple Memory System
The effects of natural or surgical lesioning certain brain regions and documenting behavioral responses in their absence is one way of discerning human dissociable memory system functions. The following provides a description of the memory retrieval characteristics of amnesiacs to give a conceptualization of how multiple memory systems are represented in the human being and how functional impairments can be behaviorally expressed.
A middle-aged woman in the turn of the century (Claparéde, 1911), in response to Korsakoff’s global amnesia, had only early childhood memory but no intermediate term memory or the ability to remember anything learned in the future. After five years of living in an asylum she did not know where she was and was unable to recognize her doctors and nurses, those with whom she saw and interacted with each and every day. One day her doctor, with whom she had been introduced many times, pricked her hand with a pin. A few hours later he again extended his hand in greeting. In response she pulled her hand away from him. Despite the fact that she was able to associate him with the pinprick, she still had no clear recollection of the event and did not know who he was or his identity. Routine introductions and social discourse were not sufficient to engender memory of individuals and respective social interactions. An uncomfortable pinprick or unconditioned stimulus (US) elicited pain or unconditioned response (UR) that made the owner of the pinprick known (conditioned stimulus-CS) through the painful handshake (conditioned response-CR). This is reflective of intact emotional stimulus-response (amygdala-striatal) learning. The inability for recognizing and/or recalling prior social interactions and personal identity reflects deficits in the structural integrity in either or both hippocampus or thalamus (Kopelman, Lasserson, Kingsley, Bello, Rush, Stanhope et al., 2001; Reed, Lasserson, Marsden, Stanhope, Stevens, Bello et al., 2003; Squire, Haist, & Shimamura, 1989) that typically characterized Korsakoff’s Syndrome.
Another study documented that amnesiacs (typically without a viable MTL region) can acquire the classical conditioned eye-blink, i.e. learn to associate a sensory stimulus (CS) and respond to it (CR) as if it were an uncomfortable (UR) puff of air (US) to the eye. But when subjects were interviewed at the conclusion of a study, they were unable to recall that they had ever participated in the conditioning experiment (Weiskrantz & Warrington, 1979). The ability for acquiring eye blink conditioning or acquisition learning can also be accompanied by the inability for intentional remembering and describing prior experience. This inability for recalling prior experience is also suggestive of hippocampal declarative deficits.
Four memory systems have been noted. Each memory system contributes its part to experience. In each system’s absence learning relating to that region’s function is impaired. Subsequent discussion will elaborate on the characteristics of memory systems.
References
Claparéde, E. (1911). Recognition and selfhood (Subsequently translated by Anne-Marie Bonnel & published in 1995). Consciousness and Cognition, 4(4), 371-8.
Kopelman, M.D., Lasserson, D., Kingsley, D., Bello, R., Rush, C., Stanhope, N., Stevens, T., Goodman, G., Heilpern, G., Kendall, B., & Colchester, A. (2001). Structural MRI volumetric analysis in patients with organic amnesia, 2: correlations with anterograde memory and executive tests in 40 patients. Journal of Neurology and Neurosurgical Psychiatry, 71(1), 23-28.
Reed, L.J., Lasserson, D., Marsden, P., Stanhope, N., Stevens, T., Bello, F., Kingsley, D., Colchester, A., & Kopelman, M.D. (2003). FDG-PET findings in the Wernicke-Korsakoff syndrome. Cortex, 39(4-5), 1027-1045.
Squire, L.R., Haist, F., & Shimamura, A.P. (1989). The neurology of memory: quantitative assessment of retrograde amnesia in two groups of amnesic patients. Journal of Neuroscience, 9(3), 828-839.
Weiskrantz, L., & Warrington, E.K. (1979). Conditioning in amnesic patients. Neuropsychologia, 17, 187-194.