title: Glutamate and GABA concentration changes in the globus pallidus internus of Parkinson's patients during performance of implicit and declarative memory tasks: a report of two subjects.
abstract: The basal ganglia, typically associated with motor function, are involved in human cognitive processes, as demonstrated in behavioral, lesion, and noninvasive functional neuroimaging studies. Here we report task-contingent changes in concentrations of the neurotransmitters glutamate (Glu) and gamma-aminobutyric acid (GABA) in the globus pallidus internus (GPi) of two patients with Parkinson's disease undergoing deep brain stimulation surgery by utilizing in-vivo microdialysis measurements during performance of implicit and declarative memory tasks. Performance of an implicit memory task (weather prediction task-WPT) was associated with increased levels of glutamate and GABA in the GPi compared to their concentrations at baseline. On the other hand, performance of a declarative memory task (verbal learning task-VLT) was associated with decreased levels of glutamate and GABA in GPi compared to baseline during the encoding and immediate recall phase with less conclusive results during the delayed recall phase. These results are in line with hypothesized changes in these neurotransmitter levels: an increase of excitatory (Glu) input from subthalamic nucleus (STN) to GPi during implicit memory task performance and a decrease of inhibitory inputs (GABA) from globus pallidus externus (GPe) and striatum to GPi during declarative memory performance. Consistent with our previous report on in-vivo neurotransmitter changes during tasks in STN, these data provide corroborative evidence for the direct involvement of basal ganglia in cognitive functions and complements our model of the functional circuitry of basal ganglia in the healthy and Parkinson's disease affected brain.
authors.affiliation: Division of Neurosurgery, Seton Brain and Spine Institute, Austin, TX, USA; Department of Psychology, University of Texas at Austin, Austin, TX, USA; University of Texas at Austin Dell Medical School, Austin, TX, USA. Electronic address: rjbuchanan@seton.org.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Buchanan
authors.affiliation: Division of Neurosurgery, Seton Brain and Spine Institute, Austin, TX, USA.
authors.forename: Klevest
authors.initials: K
authors.lastname: Gjini
authors.affiliation: Department of Neurosurgery, University of Minnesota, Minneapolis, MN, USA.
authors.forename: David
authors.initials: D
authors.lastname: Darrow
authors.affiliation: Movement Disorders Clinic, Austin, TX, USA.
authors.forename: Georgeta
authors.initials: G
authors.lastname: Varga
authors.affiliation: Department of Psychology, Auburn University, Auburn, AL, USA.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Robinson
authors.affiliation: Department of Psychology, University of Texas at Austin, Austin, TX, USA; Department of Cognitive Psychology, Eötvös Loránd University, Budapest, Hungary.
authors.forename: Zoltan
authors.initials: Z
authors.lastname: Nadasdy
mesh_terms: D000161:Acoustic Stimulation; D046690:Deep Brain Stimulation; D005260:Female; D005917:Globus Pallidus / Q000378:metabolism*; D018698:Glutamic Acid / Q000378:metabolism*; D006801:Humans; D008568:Memory; D017551:Microdialysis; D010300:Parkinson Disease / Q000378:metabolism* / Q000523:psychology; D010775:Photic Stimulation; D013067:Speech Perception; D020531:Subthalamic Nucleus / Q000378:metabolism; D014796:Visual Perception; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
chemical_list: D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid
keywords: Basal ganglia; GABA; Globus pallidus internus; Glutamate; In-vivo microdialysis; Memory tasks