Roy H. Sexton

The functional neuroanatomy of tourette's syndrome: An FDG-PET study. II: Relationships between regional cerebral metabolism and associated behavioral and cognitive features of the illness

We analyzed F-18 fluoro-deoxyglucose PET scans carried out in 18 drug-free patients with Tourettes syndrome (TS) in order to evaluate relationships between cerebral metabolism and complex cognitive and behavioral features commonly associated with this disorder. These features (obsessions and compulsions, impulsivity, coprolalia, self-injurious behavior, echophenomena, depression, and measures of attentional and visuospatial dysfunction) were associated with significant increases in metabolic activity in the orbitofrontal cortices. Similar increases, although less robust, were observed in the putamen and, in the case of attentional and visuospatial measures, in the inferior portions of the insula. On the other hand, behavioral and cognitive features were not associated with metabolic rates in other subcortical (midbrain, ventral striatum), paralimbic (parahippocampal gyrus), or sensorimotor regions (supplementary motor area, lateral premotor or Rolandic cortices), in which metabolism had, in some cases more robustly, distinguished these TS patients from controls (Braun et al., 1993). These results suggest that a subset of regions in which metabolic activity appears to be associated with the diagnosis of TS per se, may be explicitly associated with the emergence of complex behavioral and cognitive features of the illness. This is most conspicuous in the orbitofrontal cortices, and it is consistent with the observation that these features resemble the elements of a behavioral syndrome typically seen in patients with lesions of the orbitofrontal cortex.

Effects of ibotenic acid lesion of the medial prefrontal cortex on dopamine agonist-related behaviors in the rat

Behavioral responses to apomorphine and to the selective D1 and D2 dopamine receptor agonists SK&F38393 and quinpirole were evaluated in rats following ibotenic acid (IA) or sham lesion of the medial prefrontal cortex (MPFC). IA-lesioned rats showed an increased responsiveness to the postsynaptic effects of all of the dopamine agonists. Patterns of the responses to the selective agonists administered alone and in combination suggest that these effects might be due to selective increases in the sensitivity of postsynaptic D1 receptor-associated mechanisms. In addition, IA-lesioned rats pretreated with saline were hyperactive in comparison to sham-lesioned rats when animals were exposed to a novel open field, but spontaneous motor activity did not differ between these two groups when animals were pretreated with low doses (0.03 mg/kg) of quinpirole. The fact that hyperreactivity observed in lesioned animals is inhibited by a dose of quinpirole that is felt to act presynaptically, selectively attenuating endogenous dopaminergic tone, suggests that effects of the MPFC lesion may be mediated presynaptically as well.

Functional brain MR imaging based on bolus tracking with a fast T2∗-sensitized gradient-echo method

Dynamic physiological scanning, based on temporary changes in local field homogeneity during the passage of a contrast agent bolus, has been performed hitherto with echo-planar imaging (EPI) or conventional gradient-recalled techniques (FLASH). Here, it is shown that the T2* sensitivity of conventional FLASH techniques can be improved drastically on a conventional whole body instrument by delaying the gradient-echo until the subsequent TR-period without increasing total imaging time. Examples are given for a full k-space matrix (128 x 256) obtained within 2 s with a TE of 25 ms, resulting in images free of artifacts. The method is applied to bolus tracking through the brain of healthy volunteers during visual stimulation and in the dark. An average increase of regional cerebral blood volume (rCBV) in the visual cortex of 10.9% (n = 9, p = .001) was found.

Effects of large vessels in functional magnetic resonance imaging at 1.5T

To further investigate the effects of large vessels on the activation maps generated with functional magnetic resonance imaging at 1.5T, we studied activation of the human visual and motor cortex using a multitude of dedicated FLASH and echo‐planar imaging (EPI) scanning techniques. Both slice and volume scans were performed to assess relative contributions of T2* effects, in‐flow, and phase‐shift effects, specifically within and around the larger vessels (around 1 mm in diameter). The contrast mechanism in single‐slice FLASH studies appeared to be predominantly sensitive to in‐flow and phase effects of the blood water within these larger vessels, and their relative contributions were dependent on experimental parameters and vascular geometry. The contrast mechanism in gradient echo EPI studies was governed predominantly by T2* effects in tissue water (and to a lesser extent cerebrospinal fluid) surrounding the larger vessels.