Abstract
Spatial learning has been recognized over the years to be under the control of the hippocampus and related temporal lobe structures. Hippocampal damage often causes severe impairments in the ability to learn and remember a location in space defined by distal visual cues. Such cognitive disabilities are found in Parkinsonian patients. We recently investigated the role of dopamine in navigation in the 6-Hydroxy-dopamine (6-OHDA) rat, a model of Parkinson’s disease (PD) commonly used to investigate the pathophysiology of dopamine depletion (Retailleau et al., 2013). We demonstrated that dopamine (DA) is essential to spatial learning as its depletion results in spatial impairments. Our results showed that the behavioral effect of DA depletion is correlated with modification of the neural encoding of spatial features and decision making processes in hippocampus. However, the origin of these alterations in the neural processing of the spatial information needs to be clarified. It could result from a local effect: dopamine depletion disturbs directly the processing of relevant spatial information at hippocampal level. Alternatively, it could result from a more distributed network effect: dopamine depletion elsewhere in the brain (entorhinal cortex, striatum, etc.) modifies the way hippocampus processes spatial information. Recent experimental evidence in rodents, demonstrated indeed, that other brain areas are involved in the acquisition of spatial information. Amongst these, the cortex—basal ganglia (BG) loop is known to be involved in reinforcement learning and has been identified as an important contributor to spatial learning. In particular, it has been shown that altered activity of the BG striatal complex can impair the ability to perform spatial learning tasks. The present review provides a glimpse of the findings obtained over the past decade that support a dialog between these two structures during spatial learning under DA control.
Highlights
OF PARKINSON’S DISEASE, DISORIENTATION, DOPAMINE AND HIPPOCAMPUS Parkinson disease (PD) has long been characterized as a motor disease (Agid, 1991)
Amongst cognitive symptoms we can identify spatial disorientation, which has been described as an early landmark 25 years ago but left unexplored for a long time (Hovestadt et al, 1987; Taylor et al, 1989) despite its impact on life quality and public health problem (Crizzle et al, 2012)
DA innervation together with a higher liability of place fields as compared to those of CA1 (Barnes et al, 1990; Mizumori, 2006), makes Cornu Ammonis areas 3 (CA3) a good candidate for the detection of the contextual significance of spatial features (Penner and Mizumori, 2012). These facts raise the question of what happens in this brain structure when dopamine is depleted in Parkinsonian patient. We recently addressed this issue in the 6-OHDA rat, a model of PD commonly used to investigate the pathophysiology of dopamine depletion (Retailleau et al, 2013)
Summary
The Michelin red guide of the brain: role of dopamine in goal-oriented navigation. Reviewed by: Mehdi Khamassi, CNRS (Centre National de la Recherche Scientifique), France Ahmed A. Hippocampal damage often causes severe impairments in the ability to learn and remember a location in space defined by distal visual cues. Such cognitive disabilities are found in Parkinsonian patients. We demonstrated that dopamine (DA) is essential to spatial learning as its depletion results in spatial impairments. The origin of these alterations in the neural processing of the spatial information needs to be clarified It could result from a local effect: dopamine depletion disturbs directly the processing of relevant spatial information at hippocampal level. It could result from a more distributed network effect: dopamine depletion elsewhere in the brain (entorhinal cortex, striatum, etc.) modifies the way hippocampus processes spatial information. The present review provides a glimpse of the findings obtained over the past decade that support a dialog between these two structures during spatial learning under DA control
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