H Peuskens

The Processing of Visual Shape in the Cerebral Cortex of Human and Nonhuman Primates: A Functional Magnetic Resonance Imaging Study

We compared neural substrates of two-dimensional shape processing in human and nonhuman primates using functional magnetic resonance (MR) imaging in awake subjects. The comparison of MR activity evoked by viewing intact and scrambled images of objects revealed shape-sensitive regions in occipital, temporal, and parietal cortex of both humans and macaques. Intraparietal cortex in monkeys was relatively more two-dimensional shape sensitive than that of humans. In both species, there was an interaction between scrambling and type of stimuli (grayscale images and drawings), but the effect of stimulus type was much stronger in monkeys than in humans. Shape- and motion-sensitive regions overlapped to some degree. However, this overlap was much more marked in humans than in monkeys. The shape-sensitive regions can be used to constrain the warping of monkey to human cortex and suggest a large expansion of lateral parietal and superior temporal cortex in humans compared with monkeys.

Specificity of regions processing biological motion

Using functional magnetic resonance imaging and point light displays portraying six different human actions, we were able to show that several visual cortical regions, including human MT/V5 complex, posterior inferior temporal gyrus and superior temporal sulcus, are differentially active in the subtraction comparing biological motion to scrambled motion. Comparison of biological motion to three‐dimensional rotation (of a human figure), articulated motion and translation suggests that human superior temporal sulcus activity reflects the action portrayed in the biological motion stimuli, whereas posterior inferior temporal gyrus responds to the figure and hMT/V5+ to the complex motion pattern present in biological motion stimuli. These results were confirmed with implied action stimuli.

Similarities and differences in motion processing between the human and macaque brain: evidence from fMRI.

The present report reviews a series of functional magnetic resonance imaging (fMRI) activation studies conducted in parallel in awake monkeys and humans using the same motion stimuli in both species. These studies reveal that motion stimuli engage largely similar cortical regions in the two species. These common regions include MT/V5 and its satellites, of which FST contributes more to the human motion complex than is generally assumed in human imaging. These results also establish a direct link between selectivity of MT/V5 neurons for speed gradients and functional activation of human MT/V5 by three-dimensional (3D) structure from motion stimuli. On the other hand, striking functional differences also emerged: in humans V3A and several regions in the intraparietal sulcus (IPS) are much more motion sensitive than their simian counterparts.

Attention to 3-D Shape, 3-D Motion, and Texture in 3-D Structure from Motion Displays

We used fMRI to directly compare the neural substrates of three-dimensional (3-D) shape and motion processing for realistic textured objects rotating in depth. Subjects made judgments about several different attributes of these objects, including 3-D shape, the 3-D motion, and the scale of surface texture. For all of these tasks, we equated visual input, motor output, and task difficulty, and we controlled for differences in spatial attention. Judgments about 3-D shape from motion involve both parietal and occipito-temporal regions. The processing of 3-D shape is associated with the analysis of 3-D motion in parietal regions and the analysis of surface texture in occipito-temporal regions, which is consistent with the different behavioral roles that are typically attributed to the dorsal and ventral processing streams.

Changes in Cerebral CB1 Receptor Availability after Acute and Chronic Alcohol Abuse and Monitored Abstinence

Involvement of the type 1 cannabinoid receptor (CB1R) in the effects of alcohol on the brain is supported by animal experiments, but how in vivo CB1R levels are altered in alcoholic patients is still unclear. To assess the short-time effects of a binge drinking episode on CB1R availability, 20 healthy social drinkers underwent [18F]MK-9470-positron emission tomography (PET) at baseline and after intravenous ethanol administration (ALC ACU). Moreover, 26 alcoholic patients underwent sequential CB1R PET after chronic heavy drinking (ALC CHR) and after 1 month of abstinence (ALC ABST). Seventeen healthy subjects served as controls. Compared with baseline, ALC ACU resulted in a global increase of CB1R availability (+15.8%). In contrast, a global decreased CB1R availability was found in ALC CHR patients (−16.1%) compared with controls, which remained unaltered after abstinence (−17.0%). Voxel-based analysis showed that ALC CHR patients had reduced CB1R availability, especially in the cerebellum and parieto-occipital cortex. After abstinence, reduced CB1R availability extended also to other areas such as the ventral striatum and mesotemporal lobe. In conclusion, whereas the acute alcohol effect is an increase in CB1R availability, chronic heavy drinking leads to reduced CB1R availability that is not reversible after 1 month of abstinence. Longer follow-up is required to differentiate whether this is a compensatory effect of repeated endocannabinoid overstimulation or an enduring trait-like feature. An enhanced CB1R signaling may offer a new therapeutic direction for treatment of the negative affective state produced by alcohol withdrawal and abstinence, which is critical for the maintenance of alcohol addiction.

Cerebral regions processing first- and higher-order motion in an opposed-direction discrimination task

Using PET, we studied the processing of different types of motion in an opposed‐direction discrimination task. We used first‐order motion and two types of higher‐order motion (presented as moving gratings with stripes defined by flickering texture and kinetic boundaries, respectively). In these experiments, we found that all types of motion activate a common set of cortical regions when comparing a direction discrimination task to a detection of the dimming of the fixation point. This set includes left hV3A, bilateral hMT/V5+ and regions in the middle occipital gyrus, bilateral activations in the posterior and anterior parts of the intraparietal sulcus, bilateral precentral gyrus, medial frontal cortex and regions in the cerebellum. No significant differences were observed between different types of motion, even at low statistical thresholds. From this we conclude that, under our experimental conditions, the same cerebral regions are involved in the processing of first‐order and higher‐order motion in an opposed‐direction discrimination task.

Lower Limbic Metabotropic Glutamate Receptor 5 Availability in Alcohol Dependence

Animal studies suggest an important role for the metabotropic glutamate receptor subtype 5 (mGlu5) in the pathophysiology of alcohol dependence, but direct human evidence is lacking. The goal of this study was to investigate cerebral mGlu5 availability in alcohol-dependent subjects versus controls using 18F-3-fluoro-5-[(pyridin-3-yl)ethynyl]benzonitrile (18F-FPEB) PET. Methods: Dynamic 90-min 18F-FPEB scans combined with arterial blood sampling were acquired for 16 recently abstinent alcohol-dependent subjects and 32 age-matched controls. Regional mGlu5 availability was quantified by the 18F-FPEB total distribution volume using both a voxel-by-voxel and a volume-of-interest analysis with partial-volume effect correction. Alcohol consumption within the last 3 mo was assessed by questionnaires and by hair ethyl glucuronide analysis. Craving was assessed using the Desire for Alcohol Questionnaire. Results: mGlu5 availability was lower in mainly limbic regions of alcohol-dependent subjects than in controls (P < 0.05, familywise error–corrected), ranging from 14% in the posterior cingulate cortex to 36% in the caudate nucleus. Lower mGlu5 availability was associated with higher hair ethyl glucuronide levels for most regions and was related to a lower level of craving specifically in the middle frontal gyrus, cingulate cortex, and inferolateral temporal lobe. Conclusion: These findings provide human in vivo evidence that limbic mGlu5 has a role in the pathophysiology of alcohol dependence, possibly involved in a compensatory mechanism helping to reduce craving during abstinence.