title: Structural integrity of the substantia nigra and subthalamic nucleus predicts flexibility of instrumental learning in older-age individuals.
abstract: Flexible instrumental learning is required to harness the appropriate behaviors to obtain rewards and to avoid punishments. The precise contribution of dopaminergic midbrain regions (substantia nigra/ventral tegmental area [SN/VTA]) to this form of behavioral adaptation remains unclear. Normal aging is associated with a variable loss of dopamine neurons in the SN/VTA. We therefore tested the relationship between flexible instrumental learning and midbrain structural integrity. We compared task performance on a probabilistic monetary go/no-go task, involving trial and error learning of: "go to win," "no-go to win," "go to avoid losing," and "no-go to avoid losing" in 42 healthy older adults to previous behavioral data from 47 younger adults. Quantitative structural magnetization transfer images were obtained to index regional structural integrity. On average, both some younger and some older participants demonstrated a behavioral asymmetry whereby they were better at learning to act for reward ("go to win" > "no-go to win"), but better at learning not to act to avoid punishment ("no-go to avoid losing" > "go to avoid losing"). Older, but not younger, participants with greater structural integrity of the SN/VTA and the adjacent subthalamic nucleus could overcome this asymmetry. We show that interindividual variability among healthy older adults of the structural integrity within the SN/VTA and subthalamic nucleus relates to effective acquisition of competing instrumental responses.
authors.affiliation: Institute of Cognitive Neuroscience, University College London, London, UK; Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College London, London, UK. rumana.chowdhury1979@gmail.com
authors.forename: Rumana
authors.initials: R
authors.lastname: Chowdhury
authors.forename: Marc
authors.initials: M
authors.lastname: Guitart-Masip
authors.forename: Christian
authors.initials: C
authors.lastname: Lambert
authors.forename: Raymond J
authors.initials: RJ
authors.lastname: Dolan
authors.forename: Emrah
authors.initials: E
authors.lastname: Düzel
mesh_terms: D000368:Aged; D000375:Aging / Q000473:pathology* / Q000502:physiology*; D003216:Conditioning, Operant / Q000502:physiology*; D005106:Exploratory Behavior / Q000502:physiology; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D012044:Regression Analysis; D013378:Substantia Nigra / Q000473:pathology* / Q000502:physiology*; D020531:Subthalamic Nucleus / Q000473:pathology* / Q000502:physiology*; D011795:Surveys and Questionnaires; D013647:Task Performance and Analysis
keywords: Aging; Instrumental learning; Magnetization transfer; Novelty seeking; Substantia nigra