Premotor Gray Matter Volume is Associated with Clinical Findings in Idiopathic and Genetically Determined Parkinson's Disease.

In the present voxel-based morphometric study, we investigated whether the severity and duration of disease are associated with alterations in gray matter volume (GMV) in symptomatic Parkin mutation carriers (sPARKIN-MC) and patients with idiopathic Parkinson's disease (iPD). Regression analyses revealed different negative correlations between GMV in cortical motor areas and the severity as well as the disease duration in sPARKIN-MC and iPD patients. SPARKIN-MC showed a less involvement of cortical motor areas, in particular in the supplementary motor area (SMA) than iPD patients. Specifically, in iPD patients, but not in sPARKIN-MC, there was a negative correlation between the SMA degeneration and the UPDRS-II item freezing. The different degeneration patterns may mirror diverse kinetics of the disease progress in these two groups of PD patients with different underlying etiologies.

Patterns of relative cerebral blood flow in minor cognitive motor disorder in human immunodeficiency virus infection.

Individuals infected with HIV are at risk to develop cognitive impairment during the course of their disease. Although many patients develop an HIV-associated dementia, others may develop the less severe minor cognitive motor disorder (MCMD). In this study, relative cerebral blood flow was measured with PET imaging in HIV+ MCMD patients, HIV+ control subjects, and HIV- control subjects; analyses were performed by using statistical parametric mapping. Comparing a short-term memory task versus a rest state yielded activation in superior temporal cortex, postcentral gyrus, and cerebellum in all three subject groups. Comparing long- and short-term memory tasks yielded activation throughout the frontal cortex, including BA46. Activation in this area was reduced in the HIV+ control subjects and further reduced in the MCMD+ patients. Thus, brain activation associated with lower-level, automatic processing appears normal in HIV+ MCMD+ subjects, but activation associated with effortful retrieval and organizational processes is abnormal.

Speed-dependent responses in V5: A replication study.

In a previous paper, we used fMRI to examine motion-sensitive responses in human area V5 as a function of stimulus speed. As predicted by electrophysiological findings, we observed optimal responses at intermediate speeds of around 7 to 30 degrees /s. These results revealed a nonlinear (inverted "U") dependency on speed that was also evident in V3a. In this paper we repeated the experiment using an improved stimulus and a larger range of speeds. We replicated our previous findings and extended our characterization of speed-dependent responses: Optimal responses were seen in V5 at speeds of 4 and 8 degrees /s and in V3a at speeds of 4 to 16 degrees /s. We were also able to show an interaction between speed (fast vs slow) and contrast (color > luminance) in V5. This interaction was anticipated on the basis of the different properties of the geniculate and extrageniculate inputs to V5. Finally, we were also able to demonstrate an interaction between motion (moving vs stationary) and contrast (color > luminance) in V4. This suggests that for V4, color-specific responses are augmented in the context of motion; or equivalently, that color contrast enhances any motion-sensitive responses in V4.

Multiple somatotopic representations in the human cerebellum.

The classic view of representation in the cerebellum assumes two homunculi, one in the anterior lobe and one in the posterior lobe. Functional imaging has confirmed this somatotopy in the human anterior lobe but not, so far, in the posterior lobe. Using fMRI, we found separate peaks of activation for finger and toe in three ipsilateral cerebellar regions. In both the anterior and posterior lobe, the toe representation was semicircular around the finger area, with peaks of activation aligned in accord with the classic homunculi. Also, segregated peaks of activation were found in the pyramis vermis. These results confirm the existence of a second homunculus in the posterior lobe of the human cerebellum and suggest a third one.

Speed-dependent motion-sensitive responses in V5: an fMRI study.

This fMRI study examined motion-sensitive responses in human area V5 as a function of stimulus speed. Consistent with electrophysiological findings, we observed optimal responses at intermediate speeds of around 7 degrees/s to 30 degrees/s. The results are consistent with a nonlinear (inverted "U") dependency on speed that was also observed in V3a. V1 activation was observed to decrease linearly as speed increased. This is consistent with the fact that speed-sensitive cells in V1 have been shown to be tuned to much slower speeds than in V5.

Psychophysiological and modulatory interactions in neuroimaging.

In this paper we introduce the idea of explaining responses, in one cortical area, in terms of an interaction between the influence of another area and some experimental (sensory or task-related) parameter. We refer to these effects as psychophysiological interactions and relate them to interactions based solely on experimental factors (i.e., psychological interactions), in factorial designs, and interactions among neurophysiological measurements (i.e., physiological interactions). We have framed psychophysiological interactions in terms of functional integration by noting that the degree to which the activity in one area can be predicted, on the basis of activity in another, corresponds to the contribution of the second to the first, where this contribution can be related to effective connectivity. A psychophysiological interaction means that the contribution of one area to another changes significantly with the experimental or psychological context. Alternatively these interactions can be thought of as a contribution-dependent change in regional responses to an experimental or psychological factor. In other words the contribution can be thought of as modulating the responses elicited by a particular stimulus or psychological process. The potential importance of this approach lies in (i) conferring a degree of functional specificity on this aspect of effective connectivity and (ii) providing a model of modulation, where the contribution from a distal area can be considered to modulate responses to the psychological or stimulus-specific factor defining the interaction. Although distinct in neurobiological terms, these are equivalent perspectives on the same underlying interaction. We illustrate these points using a functional magnetic resonance imaging study of attention to visual motion and a position emission tomography study of visual priming. We focus on interactions among extrastriate, inferotemporal, and posterior parietal regions during visual processing, under different attentional and perceptual conditions.