19 research outputs found
Role of the Perigenual Anterior Cingulate and Orbitofrontal Cortex in Contingency Learning in the Marmoset.
Two learning mechanisms contribute to decision-making: goal-directed actions and the "habit" system, by which action-outcome and stimulus-response associations are formed, respectively. Rodent lesion studies and human neuroimaging have implicated both the medial prefrontal cortex (mPFC) and the orbitofrontal cortex (OFC) in the neural basis of contingency learning, a critical component of goal-directed actions, though some published findings are conflicting. We sought to reconcile the existing literature by comparing the effects of excitotoxic lesions of the perigenual anterior cingulate cortex (pgACC), a region of the mPFC, and OFC on contingency learning in the marmoset monkey using a touchscreen-based paradigm, in which the contingent relationship between one of a pair of actions and its outcome was degraded selectively. Both the pgACC and OFC lesion groups were insensitive to the contingency degradation, whereas the control group demonstrated selectively higher performance of the nondegraded action when compared with the degraded action. These findings suggest the pgACC and OFC are both necessary for normal contingency learning and therefore goal-directed behavior.This research was supported by a Programme Grant [G0901884] from the Medical Research Council UK (MRC) to ACR, and a Wellcome Trust Senior Investigator Award [104631 /Z/14/Z] to TWR. SAWJ was supported by a BCNI-MRC studentship. The authors wish to thank C. H Parkinson and R. Underwood for preparation of the histological material. T.W.R. consults for Cambridge Cognition, Lilly, Lundbeck, Teva, Shire Pharmaceuticals and Merck, Sharp and Dohme. He has received research grants from Lilly, Lundbeck and GSK. The remaining authors have no potential competing financial interests to disclose.This is the final version of the article. It first appeared from Oxford University Press via http://dx.doi.org/10.1093/cercor/bhw06
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Selective Role of the Putamen in Serial Reversal Learning in the Marmoset.
Fronto-striatal circuitry involving the orbitofrontal cortex has been identified as mediating successful reversal of stimulus-outcome contingencies. The region of the striatum that most contributes to reversal learning remains unclear, with studies in primates implicating both caudate nucleus and putamen. We trained four marmosets on a touchscreen-based serial reversal task and implanted each with cannulae targeting both putamen and caudate bilaterally. This allowed reversible inactivation of the two areas within the same monkeys, but across separate sessions, to directly investigate their respective contributions to reversal performance. Behavioral sensitivity to the GABAA agonist muscimol varied across subjects and between brain regions, so each marmoset received a range of doses. Intermediate doses of intra-putamen muscimol selectively impaired reversal performance, leaving the baseline discrimination phase unchanged. There was no effect of low doses and high doses were generally disruptive. By contrast, low doses of intra-caudate muscimol improved reversal performance, while high doses impaired both reversal and baseline discrimination performance. These data provide evidence for a specific role of the putamen in serial reversal learning, which may reflect the more habitual nature of repeated reversals using the same stimulus pair
INCLUSIVE PI(+/-), K+/- AND (P,(P)OVER-BAR) DIFFERENTIAL CROSS-SECTIONS AT THE Z-RESONANCE
Inclusive pi(+/-), K-+/- and (p, (p) over bar) differential cross-sections in hadronic decays of the Z have been measured as a function of z = p(hadron)/p(beam), the scaled momentum. The results are based on approximately 520 000 events measured by the ALEPH detector at LEP during 1992. Charged particles are identified bp their rate of ionization energy loss in the ALEPH Time Projection Chamber. The position, xi*, of the peak in the ln(1/z) distribution is determined, and the evolution of the peak position with centre-of-mass energy is compared with the prediction of QCD