Implicit (Nondeclarative) Memory & the MTL
The hippocampal region (included in the medial temporal lobe (MTL) region) also enhances implicit cue-in-context and object-in-scene relations (Eichenbaum, 1999). It supports early perceptual learning by processing novel physical features of perceptual stimuli (Strange, Fletcher, Henson, Friston, & Dolan, 1999) and implicit sequence learning (Schendan, Searl, Melrose, & Stern, 2003). In motor sequence learning it later facilitates recognition of previously encountered sequences (Muller, Kleinhans, Pierce, Kemmotsu, & Courchesne, 2002). The hippocampal region supports implicit perceptual learning when learning conditions are compromised by temporal brevity (Degonda, Mondadori, Bosshardt, Schmidt, Boesiger, Nitsch, et al., 2005) and perceptual noise patterns (Henke, Treyer, Nagy, Kneifel, Dursteler, Nitsch, & Buck, 2003). Finally it facilitates the detection of the hidden rule underlying complex perceptual relational processing (Rose, Haider, Weiller, & Buchel, 2002, 2004). Therefore the hippocampal region helps to support both implicit memory processing that is not in conscious awareness and explicit purposeful memory processing.
In summary, the hippocampal region plays a supportive role in implicit and nondeclarative learning and memory, by processing novelty information and enabling successful later recognition of perceptual information. It also supports learning when the conscious perception of stimuli is impaired and when increasing cognitive demands necessitate complex perceptual relational processing.
References
Degonda, N., Mondadori, C.R., Bosshardt, S., Schmidt, C.F., Boesiger, P., Nitsch, R.M., Hock, C., & Henke, K. (2005). Implicit associative learning engages the hippocampus and interacts with explicit associative learning. Neuron, 46(3), 505-520.
Eichenbaum, H. (1999). Conscious awareness, memory, and the hippocampus. Nature Neuroscience, 2(9), 775-776.
Henke, K., Treyer, V., Nagy, E.T., Kneifel, S., Dursteler, M., Nitsch, R.M., & Buck, A. (2003). Active hippocampus during nonconscious memories. Conscious Cognition, 12(1), 31-48.
Muller, R.A., Kleinhans, N., Pierce, K., Kemmotsu, N., & Courchesne, E. (2002). Functional MRI of motor sequence acquisition: effects of learning stage and performance. Brain Research Cognitive Brain Research, 14(2), 277-293.
Rose, M., Haider, H., Weiller, C., & Buchel, C. (2002). The role of medial temporal lobe structures in implicit learning: an event-related fMRI study. Neuron, 36(6), 1221-1231.
Rose, M., Haider, H., Weiller, C., & Buchel, C. (2004). The relevance of the nature of learned associations for the differentiation of human memory systems. Learning & Memory, 11(2), 145-152.
Schendan, H.E., Searl, M.M., Melrose, R.J., & Stern, C.E. (2003). An fMRI study of the role of the medial temporal lobe in implicit and explicit sequence learning. Neuron, 37(6), 1013-1025.
Strange, B.A., Fletcher, P.C., Henson, R.N., Friston, K.J., & Dolan, R.J. (1999). Segregating the functions of human hippocampus. Proceedings of National Academy of Sciences U.S.A., 96(7), 4034-4039.