ROLE OF THE BASAL GANGLIA IN LANGUAGE AND SEMANTICS: SUPPORTING CAST

1. ROLE OF THE BASAL GANGLIA IN LANGUAGE AND SEMANTICS: SUPPORTING CAST BIRC scientists continue to model basal ganglia functions in language. These functions rely upon the basal ganglia’s role in both intention and attention. Four lines of evidence contribute to current theory1: (1) Work by Nambu et al.2,3 suggests that basal ganglia activity during motor functions leads to a wave of behavioral suppression, a wave of behavioral enhancement, and finally, a second wave of behavioral suppression. Respectively, this sequence allows the animal to stop ongoing behavior, enhance the next action selected for execution, and suppress competing behaviors. The first wave of suppression appears to be controlled by a “hyperdirect” closed loop from motor cortex through the subthalamic nucleus and internal globus pallidus (Fig 1: green, black). The wave of enhancement is the product of a “direct” closed loop from motor cortex through the striatum, internal globus pallidus, and thalamus (Fig 1: red, black). The second wave of suppression is influenced by an “indirect” closed loop from the motor cortex through the striatum, external globus pallidus, subthalamic nucleus, internal globus pallidus, and thalamus (Fig 1: blue, black). (2) The literature on D1 receptors in the direct loop suggests that they facilitate activity in the direct pathway by facilitating transition to and prolonging a state in which striatal output neurons fire (see O’Donnell4 for review). (3) Research by Copland et al.5,6,7 indicates that the basal ganglia play a role in enhancing and suppressing lexical activation during semantic priming. (4) A recent study by Crosson et al.8 (2003) indicates that left pre-SMA, the left dorsal caudate nucleus, and the left ventral anterior thalamus play a role in generation of words but not generation of nonsense syllables (Fig 2). Further, left pre-SMA may use the right basal ganglia to suppress right frontal activity during word generation to keep it from interfering with left frontal activity. Thus, basal ganglia activity may enhance the efficiency of word retrieval through cycles of suppression, enhancement, and suppression. See Crosson et al. (in press) for details of the theory. Currently, BIRC scientists are testing this theory. Stay tuned!!! Figure 1 Figure 2 References 1. Crosson, Benjamin, Levy. (in press). In Hart & Kraut (eds.), Neural Basis of Semantic Memory. New York: Cambridge. 2. Nambu et al. 2000. J Neurophys. 84:289-300. 3. Nambu, Tokuno, Takada. 2002. Neurosci Res. 43:111-117. 4. O’Donnell. 2003. Eur J Neurosci. 17:429-435. 5. Copland. 2000. A Real-Time Examination of Lexical Ambiguity Resolution Following Lesions of the Dominant Nonthalamic Subcortex. Doct Thesis: U Qld, Brisbane, Australia. 6. Copland. 2003. J Internat Neuropsych Soc. 9:1041-1052. 7. Copland, Chenery, Murdoch. 2000. Neuropsychology. 14:370-390. 8. Crosson et al. 2005. J Cog Neurosci. 17:392-406.