1: Cereb Cortex. 2004 Sep;14(9):1022-30. Epub 2004 Apr 27. 
 
Motivation-dependent responses in the human caudate nucleus.
 
Delgado MR, Stenger VA, Fiez JA.
 
Department of Psychology, New York University, New York, NY 10003, USA.
m.delgado@nyu.edu
 
Motivation is a complex process that leads to completion or avoidance of a
behavior. Past research strongly implicates the basal ganglia in a circuit
integral for the control of motivation. Specifically, the human striatum has
been shown to process reward information, differentiating between monetary
rewards and punishments in recent neuroimaging experiments. It is unclear,
however, how the dorsal striatum, particularly the caudate nucleus, responds to
changes in the motivational context of a task. Using an event-related design,
where participants were given positive and negative feedback upon guessing the
value of an unknown card, we manipulated the motivational context of the task by
dividing trials into periods of high incentive (where visual feedback indicated
monetary rewards and punishments) and low incentive (where visual feedback
indicated only accuracy). We found that activity in the caudate nucleus was
strongly influenced by the different incentive periods. The hemodynamic response
was characterized by a larger rise at the onset of trials and larger differences
between positive and negative feedback during periods of high incentive. These
results suggest that changes in motivation are capable of modulating basal
ganglia activity, and further support an important role for the caudate nucleus
in affective processing.
 
PMID: 15115748 [PubMed - in process]
 
 
 
2: Proc Natl Acad Sci U S A. 2004 Sep 7;101(36):13124-31. Epub 2004 Aug 26. 
 
The learning curve: implications of a quantitative analysis.
 
Gallistel CR, Fairhurst S, Balsam P.
 
Rutgers Center for Cognitive Science, 152 Frelinghuysen Road, Piscataway, NJ
08854-8020, USA. galliste@ruccs.rutgers.edu
 
The negatively accelerated, gradually increasing learning curve is an artifact
of group averaging in several commonly used basic learning paradigms (pigeon
autoshaping, delay- and trace-eye-blink conditioning in the rabbit and rat,
autoshaped hopper entry in the rat, plus maze performance in the rat, and water
maze performance in the mouse). The learning curves for individual subjects show
an abrupt, often step-like increase from the untrained level of responding to
the level seen in the well trained subject. The rise is at least as abrupt as
that commonly seen in psychometric functions in stimulus detection experiments.
It may indicate that the appearance of conditioned behavior is mediated by an
evidence-based decision process, as in stimulus detection experiments. If the
appearance of conditioned behavior is taken instead to reflect the increase in
an underlying associative strength, then a negligible portion of the function
relating associative strength to amount of experience is behaviorally visible.
Consequently, rate of learning cannot be estimated from the group-average curve;
the best measure is latency to the onset of responding, determined for each
subject individually.
 
PMID: 15331782 [PubMed - in process]
 
 
 
3: Proc Natl Acad Sci U S A. 2004 Sep 7;101(36):13335-40. Epub 2004 Aug 30. 
 
Changes in connectivity profiles define functionally distinct regions in human
medial frontal cortex.
 
Johansen-Berg H, Behrens TE, Robson MD, Drobnjak I, Rushworth MF, Brady JM,
Smith SM, Higham DJ, Matthews PM.
 
Oxford Centre for Functional Magnetic Resonance Imaging of the Brain, University
of Oxford, John Radcliffe Hospital, Oxford OX3 9DU, United Kingdom.
heidi@fmrib.ox.ac.uk
 
A fundamental issue in neuroscience is the relation between structure and
function. However, gross landmarks do not correspond well to microstructural
borders and cytoarchitecture cannot be visualized in a living brain used for
functional studies. Here, we used diffusion-weighted and functional MRI to test
structure-function relations directly. Distinct neocortical regions were defined
as volumes having similar connectivity profiles and borders identified where
connectivity changed. Without using prior information, we found an abrupt
profile change where the border between supplementary motor area (SMA) and
pre-SMA is expected. Consistent with this anatomical assignment, putative SMA
and pre-SMA connected to motor and prefrontal regions, respectively. Excellent
spatial correlations were found between volumes defined by using connectivity
alone and volumes activated during tasks designed to involve SMA or pre-SMA
selectively. This finding demonstrates a strong relationship between structure
and function in medial frontal cortex and offers a strategy for testing such
correspondences elsewhere in the brain.
 
PMID: 15340158 [PubMed - in process]
 
 
 
4: Cereb Cortex. 2004 Oct;14(10):1153-63. Epub 2004 May 13. 
 
Parieto-premotor areas mediate directional interference during bimanual
movements.
 
Wenderoth N, Debaere F, Sunaert S, van Hecke P, Swinnen SP.
 
Motor Control Lab, Group Biomedical Sciences, KU Leuven, Belgium.
nicole.wenderoth@flok.kuleuven.ac.be
 
In bimanual movements, interference emerges when limbs are moved simultaneously
along incompatible directions. The neural substrate and mechanisms underlying
this phenomenon are largely unknown. We used functional magnetic resonance
imaging to compare brain activation during directional incompatible versus
compatible bimanual movements. Our main results were that directional
interference emerges primarily within superior parietal, intraparietal and
dorsal premotor areas of the right hemisphere. The same areas were also
activated when the unimanual subtasks were executed in isolation. In light of
previous findings in monkeys and humans, we conclude that directional
interference activates a parieto-premotor circuit that is involved in the
control of goal-directed movements under somatosensory guidance. Moreover, our
data suggest that the parietal cortex might represent an important locus for
integrating spatial aspects of the limbs' movements into a common action. It is
hypothesized to be the candidate structure from where interference arises when
directionally incompatible movements are performed. We discuss the possibility
that interference emerges when computational resources in these parietal areas
are insufficient to code two incompatible movement directions independently from
each other.
 
PMID: 15142955 [PubMed - in process]
 
 
 
5: Proc Natl Acad Sci U S A. 2004 Sep 7;101(36):13363-7. Epub 2004 Aug 30. 
 
Enhanced neurogenesis in Alzheimer's disease transgenic (PDGF-APPSw,Ind) mice.
 
Jin K, Galvan V, Xie L, Mao XO, Gorostiza OF, Bredesen DE, Greenberg DA.
 
Buck Institute for Age Research, Novato, CA 94945, USA.
 
Neurogenesis continues in the adult brain and is increased in certain
pathological states. We reported recently that neurogenesis is enhanced in
hippocampus of patients with Alzheimer's disease (AD). We now report that the
effect of AD on neurogenesis can be reproduced in a transgenic mouse model.
PDGF-APP(Sw,Ind) mice, which express the Swedish and Indiana amyloid precursor
protein mutations, show increased incorporation of BrdUrd and expression of
immature neuronal markers in two neuroproliferative regions: the dentate gyrus
and subventricular zone. These changes, consisting of approximately 2-fold
increases in the number of BrdUrd-labeled cells, were observed at age 3 months,
when neuronal loss and amyloid deposition are not detected. Because enhanced
neurogenesis occurs in both AD and an animal model of AD, it seems to be caused
by the disease itself and not by confounding clinical factors. As neurogenesis
is increased in PDGF-APP(Sw,Ind) mice in the absence of neuronal loss, it must
be triggered by more subtle disease manifestations, such as impaired
neurotransmission. Enhanced neurogenesis in AD and animal models of AD suggests
that neurogenesis may be a compensatory response and that measures to enhance
neurogenesis further could have therapeutic potential.
 
PMID: 15340159 [PubMed - in process]