Basal ganglia and memory

Packard MG and Knowlton BJ. Learning and memory functions of the basal ganglia. Annu Rev. Neurosci. 2002; 25:563-593. This article reviews the role of the basal ganglia, especially the dorsal striatum, in learning and memory. The hypothesis is that the basal ganglia mediates a form of learning in which stimulus-response (S-R) associations or habits are acquired. These can be dissociated from the cognitive or declarative medial temporal lobe memory systems invluding the hippocampus. During learning, the two systems maybe activated simultaneously and competitively inhibit each other.
Tibits picked up from the article:
1. Wise et al. (1996 Crit Rev Neurobiol) hypothesized that the frontostriatocortical loops train the cortex to produce learned responses in the presence of patterned sensory information.

2. Neurochemically dopaminergic input from the substantia nigra and ventral tegmentum innervate the dorsal and ventral striatum, whereas glutamatergic input from cortex, thalamus, amygdala and hippocampus are excitatory. Gaba-ergic output from medium spiny neurons in neostriatum exist, and interneurons, many are cholinergic.

3. The "patch" compartment of the striatum (striosomes) have low Ach, and high opiates and substance P. The matrix compartment has cholinergic and somatostatin containing neurons. Dopaminergic input from the ventral tegmentum innervates primarily patch, whereas dopaminergic input from SN innervates primarily matrix. Amygdala and hippocampus innervate primarily patch, whereas cortex and thalamus innervate primarily matrix. White et al. hypothesize that the matrix primarily mediates mnemonic functions (1989 Life Sci).

4. In rats, a win-shift and win-stay model double dissociates. Dorsal striatal lesions impair win stay and hippocampal-fimbriae-fornix lesions impair win shift model (win stay measures working memory; rats have to visit each bay once to get reward; win shift requires them to learn to visit a bay with a stimulus eg a light). With reinforcer devaluation (pair food reward with nauseating lithium chloride injections) rats continue to approach illuminated bays. This suggests the caudate win stay task involves acqusition of a S-R (light approach) not a stimulus-stimulus (light food) reward behavior.