Herbert Bauer

Cholecystokinin decreases appetite and activation evoked by stimuli arising from the preparation of a meal in man

Abstract Cholecystokinin (CCK) serves as a satiety signal in rats and rhesus monkeys. This study attempts to determine whether CCK plays such a role also in man. Sixteen healthy young non-obese subjects after an overnight fast were infused in double blind fashion with 180 ml/30 min of either (1) saline, (2) 0.6, (3) 3.0, or (4) 6.0 Ivy U 95% pure porcine CCK (GIH Stockholm)/kg body wt dissolved in saline. Appetite was stimulated by the smells and sounds arising from the preparation of a meal in the subjects presence. Subjective reports of “hunger” and “voraciousness” in a self-rating scale increased after appetite stimulation and saline infusion but decreased with increasing dose of CCK. Reports of activation (“activated,” “awake”, “fresh”, “enterprising”) as well as objective activation measures (sensorimotor performance, heart rate, heart rate variability, and Alpha-to-Theta ratio in the EEG) increased after appetite stimulation and saline but decreased with increasing dose of CCK, thus reminiscent of postprandial satiety and deactivation. In conclusion, CCK seems to be involved also in the mechanisms eliciting satiety in man.

Technical requirements for high-quality scalp DC recordings

An easily applicable procedure for obtaining high-quality scalp DC recordings is described. A sophisticated amplifier technique, skin potential reduction and stabilisation of electrode potential make up this procedure.

Evidence for Premotor Cortex Activity during Dynamic Visuospatial Imagery from Single-Trial Functional Magnetic Resonance Imaging and Event-Related Slow Cortical Potentials

A strong correspondence has been repeatedly observed between actually performed and mentally imagined object rotation. This suggests an overlap in the brain regions involved in these processes. Functional neuroimaging studies have consistently revealed parietal and occipital cortex activity during dynamic visuospatial imagery. However, results concerning the involvement of higher-order cortical motor areas have been less consistent. We investigated if and when premotor structures are active during processing of a three-dimensional cube comparison task that requires dynamic visuospatial imagery. In order to achieve a good temporal and spatial resolution, single-trial functional magnetic resonance imaging (fMRI) and scalp-recorded event-related slow cortical potentials (SCPs) were recorded from the same subjects in two separate measurement sessions. In order to reduce inter-subject variability in brain activity due to individual differences, only male subjects (n = 13) with high task-specific ability were investigated. Functional MRI revealed consistent bilateral activity in the occipital (Brodmann area BA18/19) and parietal cortex (BA7), in lateral and medial premotor areas (BA6), the dorsolateral prefrontal cortex (BA9), and the anterior insular cortex. The time-course of SCPs indicated that task-related activity in these areas commenced approximately 550-650 ms after stimulus presentation and persisted until task completion. These results provide strong and consistent evidence that the human premotor cortex is involved in dynamic visuospatial imagery.

Altered reward processing in the nucleus accumbens and mesial prefrontal cortex of patients with posttraumatic stress disorder.

Posttraumatic stress disorder (PTSD) is known to be associated with altered medial prefrontal activation in response to threatening stimuli and with behavioural deficits in prefrontal functions such as working memory and attention. Given the importance of these areas and processes for decision-making, this functional magnetic resonance imaging study investigated whether decision-making is altered in patients with PTSD. In particular, the neural response to gain and loss feedback was evaluated in a decision-making task in which subjects could maximise their number of points total by learning a particular response pattern. Behaviourally, controls learned the correct response pattern faster than patients. Functionally, patients and controls differed in their neural response to gains, but not in their response to losses. During the processing of gains in the late phase of learning, PTSD patients as compared to controls showed lower activation in the nucleus accumbens and the mesial PFC, critical structures in the reward pathway. This reduced activation was not due to different rates of learning, since it was similarly present in patients with unimpaired learning performance. These findings suggest that positive outcome information lost its salience for patients with PTSD. This may reflect decreasing motivation as the task progressed.

Manipulation of feedback expectancy and valence induces negative and positive reward prediction error signals manifest in event-related brain potentials

The feedback-related negativity (FRN) has been hypothesized to be most sensitive to unexpected negative feedback. The present study investigated feedback expectancy and valence using a probabilistic gambling paradigm where subjects encountered expected or unexpected positive and negative feedback outcomes. In line with previous studies, FRN amplitude reflected a negative reward prediction error, but to a minor extent also a positive reward prediction error. Moreover, the P300 amplitude was largest after unexpected feedback, irrespective of valence. We propose to interpret the FRN in terms of a reinforcement learning signal which is detecting mismatch between internal and external representations indexed by the ACC to extract motivationally salient outcomes.

Cortical activity of good and poor spatial test performers during spatial and verbal processing studied with Slow Potential Topography

Whether essential processing of spatial information is lateralized asymmetrically in the human cortex is still a matter of debate. In this study, items of an Item Response Theory calibrated test for spatial ability were used to ensure stimulus homogeneity and validity. Subjects were preselected as extreme groups of good and poor spatializers. Mapping of true DC-recorded slow potential shifts (SPSs) resulted in distinctly discriminable topographies with spatial and verbal-analytic material as well as with spatial performance groups within the spatial block. Left fronto-central negativity maxima in the verbal condition clearly contrasted with occipito-parietal peak activity in the spatial condition. Poor spatializers showed higher amplitudes as well as a tendency to asymmetric activity in right parietal (parieto-temporal) areas, whereas in good spatializers the activity was localized symmetrically in occipital and occipito-parietal regions. The findings emphasize the importance of the right posterior cortex for spatial processing (negativity maxima at occipital and right parietal sites) and suggest a task-specific lower cortical efficiency or, seen from a processing perspective, a higher Investment of Cortical Effort (ICE) on the part of poor spatializers.

Using ICA for removal of ocular artifacts in EEG recorded from blind subjects

One of the standard applications of Independent Component Analysis (ICA) to EEG is removal of artifacts due to movements of the eye bulbs. Short blinks as well as slower saccadic movements are removed by subtracting respective independent components (ICs). EEG recorded from blind subjects poses special problems, since it shows a higher quantity of eye movements, which are also more irregular and very different across subjects. It is demonstrated that ICA can still be of use by comparing results from four blind subjects with results from one subject without eye bulbs who therefore does not show eye movement artifacts at all.

The functional role of dorso-lateral premotor cortex during mental rotation An event-related fMRI study separating cognitive processing steps using a novel task paradigm

Subjects deciding whether two objects presented at angular disparity are identical or mirror versions of each other usually show response times that linearly increase with the angle between objects. This phenomenon has been termed mental rotation. While there is widespread agreement that parietal cortex plays a dominant role in mental rotation, reports concerning the involvement of motor areas are less consistent. From a theoretical point of view, activation in motor areas suggests that mental rotation relies upon visuo-motor rather than visuo-spatial processing alone. However, the type of information that is processed by motor areas during mental rotation remains unclear. In this study we used event-related fMRI to assess whether activation in parietal and dorsolateral premotor areas (dPM) during mental rotation is distinctively related to processing spatial orientation information. Using a newly developed task paradigm we explicitly separated the processing steps (encoding, mental rotation proper and object matching) required by mental rotation tasks and additionally modulated the amount of spatial orientation information that had to be processed. Our results show that activation in dPM during mental rotation is not strongly modulated by the processing of spatial orientation information, and that activation in dPM areas is strongest during mental rotation proper. The latter finding suggests that dPM is involved in more generalized processes such as visuo-spatial attention and movement anticipation. We propose that solving mental rotation tasks is heavily dependent upon visuo-motor processes and evokes neural processing that may be considered as an implicit simulation of actual object rotation.

Human motor cortex activity during mental rotation.

The functional role of human premotor and primary motor cortex during mental rotation has been studied using functional MRI at 3 T. Fourteen young, male subjects performed a mental rotation task in which they had to decide whether two visually presented cubes could be identical. Exploratory Fuzzy Cluster Analysis was applied to identify brain regions with stimulus-related time courses. This revealed one dominant cluster which included the parietal cortex, premotor cortex, and dorsolateral prefrontal cortex that showed signal enhancement during the whole stimulus presentation period, reflecting cognitive processing. A second cluster, encompassing the contralateral primary motor cortex, showed activation exclusively after the button press response. This clear separation was possible in 3 subjects only, however. Based on these exploratory results, the hypothesis that primary motor cortex activity was related to button pressing only was tested using a parametric approach via a random-effects group analysis over all 14 subjects in SPM99. The results confirmed that the stimulus response via button pressing causes activation in the primary motor cortex and supplementary motor area while parietal cortex and mesial regions rostral to the supplementary motor area are recruited for the actual mental rotation process.

Operant conditioning of brain steady potential shifts in man

Steady potential shifts (SPS) recorded from the scalp were conditioned operantly by visual and acoustical feedback. Three groups of seven subjects were each tested with a different response-reinforcement contingency: positive reinforcement for a positive SPS after a cue stimulus, positive reinforcement for a negative SPS after a cue stimulus, and noncontingent reinforcement. The steady potential shifts learned under these three conditions differed significantly. Negative shifts were associated with subjective feelings of activation, positive shifts with inactivation. Cortical genesis and possible artifacts are discussed.