Processing of auditory motion in inferior parietal lobule: evidence from transcranial magnetic stimulation.

The neural substrates of auditory motion processing are, at present, still a matter of debate. It has been hypothesized that motion information is, as in the visual system, processed separately from other aspects of auditory information, such as stationary location. Here we aimed to differentiate the location of auditory motion processing in human cortex using low-frequency repetitive transcranial magnetic stimulation (rTMS) in combination with a psychophysical task of motion discrimination. rTMS was applied offline to right posterior superior temporal gyrus, right inferior parietal lobule, right dorsal premotor cortex, or right primary somatosensory cortex (as reference site). A significant decrease in performance was obtained exclusively for sounds presented in left hemispace after rTMS over the right inferior parietal lobule (BA 40). This finding indicates that the inferior parietal lobule plays a crucial role in the analysis of moving sound, with an apparent contralaterality of cortical processing. Combined with previous studies which have demonstrated effects of rTMS on static sound localization for both inferior parietal and posterior temporal cortices, the results suggest a hierarchical processing of auditory spatial information, with higher-order functions of motion analysis, such as discrimination of motion direction, mainly taking place beyond the temporal lobe.

Effects of alcohol cue exposure on response inhibition in detoxified alcohol-dependent patients.

BACKGROUND: There is evidence that exerting self-control during alcohol craving can diminish performance on subsequent tasks that require self-control. Based on the resource depletion model (Muraven and Baumeister, 2000), we examined the influence of alcohol cue exposure on detoxified alcohol-dependent patients' ability to inhibit ongoing responses. METHODS: Twenty alcohol-dependent patients were randomly assigned to an alcohol-cue exposure and a control-cue exposure condition and thereafter had to perform an inhibition task (i.e., stop-signal task). RESULTS: Participants who sniffed alcohol before performing the inhibition task reported a stronger urge to drink alcohol than the control group that sniffed water. Participants who sniffed alcohol were also impaired in their inhibitory performance but not in their noninhibitory performance on the stop-signal task. CONCLUSIONS: The urge to drink presumably reduced participants' self-control, and this interfered with their ability to inhibit responding.

Evaluation of spatial processing in virtual reality using functional magnetic resonance imaging (FMRI).

While the ecological validity of virtual reality (VR) applications is usually assessed by behavioral data or interrogation, an alternative approach on a neuronal level is offered by brain imaging methods. Because it is yet unclear if 3D space in virtual environments is processed analogically to the real world, we conducted a study investigating virtual spatial processing in the brain using functional magnetic resonance imaging (fMRI). Results show differences in VR spatial brain processing as compared to known brain activations in reality. Identifying differences and commonalities of brain processing in VR reveals limitations and holds important implications for VR therapy and training tools. When VR therapy aims at the rehabilitation of brain function and activity, differences in brain processing have to be taken into account for designing effective VR training tools. Furthermore, for an evaluation of possible restoration effects caused by VR training, it is necessary to integrate information about the brain activation networks elicited by the training. The present study provides an example for demonstrating the benefit of fMRI as an evaluation tool for the mental processes involved in virtual environments.

The dorsal premotor cortex orchestrates concurrent speech and fingertapping movements.

Human speech and hand use both involve highly specialized complex movement patterns. Whereas previous studies in detail characterized the cortical motor systems mediating speech and finger movements, the network that provides coordination of concurrent speech and hand movements so far is unknown. Using functional magnetic resonance imaging (fMRI), the present study investigated differential cortical networks devoted to speech or fingertapping, and regions mediating integration of these complex movement patterns involving different effectors. The conjunction contrasts revealing regions activated both during sole fingertapping and sole repetitive articulation or reading aloud showed contralateral regions at the border of ventral and dorsal motor cortex. In contrast, the analyses revealing regions showing a higher level of fMRI activation for concurrent movements of both effectors compared with sole hand movements or repetitive articulation or reading aloud showed distinct premotor activations, which were situated dorsal and caudal to the areas activated across speech and fingertapping tasks. These results indicate that the premotor cortex (PMC) subserves coordination of concurrent speech with hand movements. This integrative motor region is not identical with the area that shows overlapping activations for speech and fingertapping. Thus, concurrent performance of these complex movement patterns involving different effectors requires, in addition to somatotopic motor cortex activation, orchestration subserved by a distinct PMC area.

The role of the anterior intraparietal sulcus in crossmodal processing of object features in humans: an rTMS study.

Investigations in macaques and humans have shown that the anterior intraparietal sulcus (IPS) has an important function in the integration of information from tactile and visual object manipulation. The goal of this study was to investigate the special functional role of the anterior IPS in visuo-tactile matching in humans. We used the "virtual-lesion" technique of repetitive transcranial magnetic stimulation (rTMS) to test the functional relevance of anterior IPS for visuo-tactile crossmodal matching. Two crossmodal (visual encoding and tactile recognition and vice versa) and two unimodal delayed matching-to-sample tests with geometrical patterns were performed by 12 healthy subjects. We determined error rates before and after focal low-frequency rTMS applied over the left anterior IPS, right anterior IPS and vertex. During the manipulation of objects with the right hand, rTMS over the left anterior IPS induced a significant deterioration for visual encoding and tactile recognition, but not for tactile encoding and visual recognition. For the visual and tactile unimodal conditions, no significant alterations in task performance were found. rTMS application over right IPS when manipulating objects with the left hand did not affect crossmodal task performance. In conclusion, we have demonstrated an essential functional role of the left anterior IPS for visuo-tactile matching when manipulating objects with the right hand. However, we found no clear evidence for left IPS involvement in tactile encoding and visual recognition. The differential effect of rTMS on tactile and visual encoding and recognition are not consistently explained by previous concepts of visuo-tactile integration.

Limbic event-related potentials to words and pictures in the presurgical evaluation of temporal lobe epilepsy.

We recorded limbic event-related potentials (ERPs) with intrahippocampal depth electrodes in a more demanding verbal and an easier pictorial continuous recognition task in patients undergoing presurgical evaluations of their medical refractory mesial temporal lobe epilepsies (MTLE). In all cases depth electrodes were implanted because non-invasive studies could not demonstrate unilateral seizure-onset unequivocally. For the present study we only considered 24 patients who eventually were found to suffer from unilateral MTLE, in whom hippocampal sclerosis (HS) was confirmed histologically, and who were seizure-free post-operatively. We found that the rhinal anterior medial temporal lobe N400 (AMTL-N400) to first presentations of words but not to pictures was reduced in amplitude on the side of seizure origin. Our data suggest that limbic ERPs to words are more sensitive to the epileptogenic process than those to pictures. Thus, if limbic ERPs are recorded as part of invasive presurgical evaluations, verbal instead of pictorial recognition paradigms should be employed.

Smoking and structural brain deficits: a volumetric MR investigation.

Growing evidence from animal studies indicates brain-damaging properties of nicotine exposure. Investigations in humans found a wide range of functional cerebral effects of nicotine and cigarette smoking, but studies focusing on brain damage are sparse. In 22 smokers and 23 never-smokers possible differences of the cerebral structures were investigated using magnetic resonance imaging and voxel-based morphometry. Significantly smaller grey matter volume and lower grey matter density (P = 0.05, corrected) were observed in the frontal regions (anterior cingulate, prefrontal and orbitofrontal cortex), the occipital lobe and the temporal lobe including parahippocampal gyrus, in smokers than in never-smokers. Group differences of either grey matter volume or grey matter density were also found in the thalamus, cerebellum and substantia nigra, among other regions. Smokers did not show greater volumes than never-smokers in any cerebral region. Magnitude of lifetime exposure to tobacco smoke (pack-years) was inversely correlated with volume of frontal and temporal lobes and cerebellum (P = 0.001, uncorrected). The data indicate structural deficits of several cortical and subcortical regions in smokers relative to never-smokers. The topographic profile of the group differences show some similarities to brain networks known to mediate drug reinforcement, attention and working memory processing. The present findings may explain in part the frequently reported cognitive dysfunctions in chronic cigarette consumers.

Persistent severe amnesia due to seizure recurrence after unilateral temporal lobectomy.

Anterograde amnesia is a severely disabling state which has been reported as a consequence of bilateral mesiotemporal lesions in humans. In the present paper, recurrent epileptic seizures after temporal lobectomy are described as a rare cause of severe amnesia in two patients. Diffusion-weighted MRI in one patient showed cytotoxic edema during a nonconvulsive status epilepticus and subsequent progressive hippocampal atrophy within the following month. In the other patient, repeated conventional MRI revealed no structural abnormalities in the contralateral temporal lobe.

Rhinal-hippocampal EEG coherence is reduced during human sleep.

The deficiency of declarative memory compared with waking state is an often overlooked characteristic of sleep. Here, we investigated whether rhinal-hippocampal coherence, an electrophysiological correlate of declarative memory formation, is significantly altered during sleep as compared with waking state. For this purpose, we analysed recordings of intracranial EEG activity during sleep obtained directly from within the medial temporal lobe in patients with unilateral temporal lobe epilepsy. We found a general reduction of rhinal-hippocampal EEG coherence during sleep compared with waking state, which was most pronounced within the upper gamma bands (average decrease up to 56%). The observed coherence changes clearly differ from findings reported for surface EEG data and thus appear to be specific for the medial temporal lobe. The decrease of rhinal-hippocampal EEG coherence from waking state towards sleep may yield an electrophysiological explanation for the sleep-related deficiency of declarative memory.