Jessica Piscopello & Bryan DevanJessica Piscopello & Bryan DevanLaboratory of Comparative Neuropsychology, Psychology Department, Towson University, Towson, MD 21252Laboratory of Comparative Neuropsychology, Psychology Department, Towson University, Towson, MD 21252

A variation of the water maze competitive place task (McDonald et al., 2005; Fig 1) was used to study the role of the hippocampus (HPC) and medial caudate-putamen (mCPu) (see Fig 2) in spatial navigation and higher-order [(S-S)-R] habit formation. Rats received distributed place training for 18 days (4 trials/day) with the hidden platform located in the center of the NE quadrant (location 1) followed by mass place re-training (8 trials) to a second location in the center of the SW quadrant on day 19. A probe test was given on day 20 to measure competitive place responding. Preliminary lesion findings show that HPC damage impaired spatial learning overall (Fig 3), although non-cognitive procedural strategies such as circumnavigation spared early performance during original training, consistent with Devan et al. (1996; Fig 4). Despite the extended training to the original location, controls showed a slight bias in searching at the new location on the probe test (Fig 5) suggesting that spatial working memory had a relatively strong influence over navigational behavior. In contrast, control latencies to enter the old and new locations were approximately equal, thus optimizing potential detection of behavioral changes in either direction with this performance measure (Fig 6). HPC damage also elevated latencies to enter the new location more than the old location on the competition test. Dorsomedial striatal (mCPu) damage produced a less-severe disruption of spatial performance overall and increased the latency to enter the original/old location relative to the new location on the competition test.

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FIG 1. Acquisition – hidden platform at location 1, 4 trials/day (18 days); Retraining – hidden platform moved to location 3, 2 blocks of 4 trials (day 19); Competition – platform removed, 60 sec probe test (day 20).

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Fig 3- Escape latencies during first 2 phases of the study, acquisition and retraining.

FIG 2. electrolytic mCPu lesions were conducted using the coordinates AP: +0.7 mm; ML: ± 2.4 mm; DV: 5.7 mm, relative to skull surface and bregma. The coordinates for hippocampal KA lesions were AP: - 4.0 mm; ML: ±2.5 mm; DV: -3.7 mm

Devan, B. D., Goad, E. H., & Petri, H. L. (1996). Dissociation of hippocampal and striataDevan, B. D., Goad, E. H., & Petri, H. L. (1996). Dissociation of hippocampal and striata contribution to spatial navigation in the water maze. contribution to spatial navigation in the water maze. Neurobiology of Learning and MemoryNeurobiology of Learning and Memory,, 6666, 305-323., 305-323.Devan, B. D., Hong, N. S., & McDonald, R. J. (2011). Parallel associative processing in theDevan, B. D., Hong, N. S., & McDonald, R. J. (2011). Parallel associative processing in the dorsal striatum: segregation of stimulus-response and cognitive control subregions. dorsal striatum: segregation of stimulus-response and cognitive control subregions. Neurobiology of Learning and MemoryNeurobiology of Learning and Memory, , 96(2)96(2), 95-120., 95-120.Devan, B. D., McDonald, R. J., & White, N. M. (1999). Effects of medial and lateral caudate-Devan, B. D., McDonald, R. J., & White, N. M. (1999). Effects of medial and lateral caudate- putamen lesions on place- and cue-guided behaviors in the water maze: relation toputamen lesions on place- and cue-guided behaviors in the water maze: relation to thigmotaxis. thigmotaxis. Behavioural Brain ResearchBehavioural Brain Research, , 100(1-2)100(1-2), 5-14., 5-14.Devan, B. D., & White, N. M. (1999). Parallel information processing in the dorsal striatum: Devan, B. D., & White, N. M. (1999). Parallel information processing in the dorsal striatum: relation to hippocampal function. relation to hippocampal function. Journal of NeuroscienceJournal of Neuroscience, , 19(7)19(7), 2789-2798. , 2789-2798. Divac, I., & Öberg, R. G. E. (1992). Subcortical mechanisms in cognition. In G. Vallar,Divac, I., & Öberg, R. G. E. (1992). Subcortical mechanisms in cognition. In G. Vallar, S. F. Capra, & C.-W. Wallesch (Eds.), Neuropsychological disorders associated withS. F. Capra, & C.-W. Wallesch (Eds.), Neuropsychological disorders associated with subcortical lesions (pp. 42–60). Oxford: Oxford University Press.subcortical lesions (pp. 42–60). Oxford: Oxford University Press.McDonald, R. J., Hong, N. S., Craig, L. A., Holahan, M. R., Louis, M., & Muller, R. U. (2005). McDonald, R. J., Hong, N. S., Craig, L. A., Holahan, M. R., Louis, M., & Muller, R. U. (2005). NMDA-receptor blockade by CPP impairs post-training consolidation of a rapidly acquiredNMDA-receptor blockade by CPP impairs post-training consolidation of a rapidly acquired spatial representation in rat hippocampus. spatial representation in rat hippocampus. Eur J NeurosciEur J Neurosci, , 22(5)22(5), 1201-1213. , 1201-1213. Paxinos, G., & Watson, C. (1998). Paxinos, G., & Watson, C. (1998). The rat brain in stereotaxic coorinatesThe rat brain in stereotaxic coorinates, 4th ed. San Diego: , 4th ed. San Diego: Academic Press.Academic Press.

The caudate nucleus together with related areas of the prefrontal cortex has been shown to contribute to various cognitive functions (e.g., see Divac & Öberg, 1992 for review). Previously, we have reported dissociations between the effects of dorsolateral and dorsomedial striatal lesions on cue-place versions of the water maze task (Devan et al, 1999; Devan & White, 1999). Unlike the place learning and/or cognitive-spatial memory impairments commonly reported for hippocampal lesions, the dorsolateral striatum may mediates a form of simple stimulus-response habit formation. The present findings suggest that while the hippocampus is directly involved in cognitive-spatial information processing, the dorsomedial striatum may contribute to the cognitive control of performance incrementally over time by strengthening responses based on higher-order habit formation (see Devan et al, 2011 for review).

Fig 4- Paths illustrating some of the strategies used by lesioned rats during acquisition phase.

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Fig 5- Probe test results during phase 3 competition test.

Fig 6- Probe test results during phase 3 competition test.