Multimodal motion processing in area V5/MT: evidence from an artificial class of audio-visual events.

Audio-visual integration in the human brain influences perception and precision of motor tasks. We tested audio-visual integration during height estimation when presenting video clips of counter movement jumps (CMJ), using sparse sampling fMRI at 3T. Employing the technique of "sonification", we created artificial auditory-visual motion events by transforming the ground reaction force of the CMJs into the auditory domain, modulating frequency and amplitude of the standard pitch "A" (440 Hz). We combined these "sonificated" movements with either concordant or discordant visual movement displays. We hypothesized that processing of concordant audio-visual stimuli would enhance neural activity in audio-visual integration areas. Therefore, four conditions were compared: 1. unimodal visual, 2. unimodal auditory, 3. auditory+visual concordant, and 4. auditory+visual discordant. The unimodal conditions, when compared against each other, resulted in expected activation maxima in primary visual and auditory cortex, respectively. Enhanced activation was found in area V5/MT bilaterally for the concordant multimodal, as compared to both unimodal, conditions. This effect was specific for the concordant bimodal condition, as evidenced by a direct comparison between concordant and discordant bimodal conditions. Using "sonification", we provide evidence that area V5/MT is modulated by concordant auditory input, albeit the artificial nature of the stimuli, which argues for a role of this region in multimodal motion integration, beyond the pure visual domain. This may explain previous behavioral evidence of facilitatory effects exerted by auditory motion stimuli on the perception of visual motion, and may provide the basis for future applications in motor learning and rehabilitation.

Differences of cerebral activation between superior and inferior learners during motor sequence encoding and retrieval.

Cerebral activation during memory encoding and retrieval might depend on subjects' learning capacity, either by corresponding to better performance in superior learners or by reflecting increased effort in inferior learners. To investigate these alternative hypotheses, the study compared cerebral activation during encoding and retrieval of a motor sequence in groups of subjects with superior and inferior learning performances. Ten healthy subjects underwent functional magnetic resonance imaging (fMRI) while performing a motor sequence encoding paradigm (i.e. finger tapping sequence) and a retrieval paradigm (i.e. reproduction of the learned sequence). Subjects were divided into superior and inferior learners according to the correctness of sequence reproduction during retrieval. During encoding, there was strong bilateral activation in the middle frontal gyrus, the supplementary motor area (SMA), the lateral parietal lobe and the cerebellum. During retrieval, again strong activation was found in identical areas of the prefrontal cortex, the parietal lobe and the cerebellum. During encoding, inferior learners showed more left-sided activations in the left middle frontal and inferior parietal gyri. Superior learners showed increased activation in the corresponding right-sided brain areas during encoding as well as during retrieval. Differences of cerebral activations in the prefrontal and parietal cortex during encoding and retrieval were found to be related to retrieval performance, i.e. success and effort. Further intervention studies are needed to assess whether these interindividual differences are the cause or the consequence of differences in memory performance.

Response-related fMRI of veridical and false recognition of words.

OBJECTIVES: Studies on the relation between local cerebral activation and retrieval success usually compared high and low performance conditions, and thus showed performance-related activation of different brain areas. Only a few studies directly compared signal intensities of different response categories during retrieval. During verbal recognition, we recently observed increased parieto-occipital activation related to false alarms. The present study intends to replicate and extend this observation by investigating common and differential activation by veridical and false recognition. METHODS: Fifteen healthy volunteers performed a verbal recognition paradigm using 160 learned target and 160 new distractor words. The subjects had to indicate whether they had learned the word before or not. Echo-planar MRI of blood-oxygen-level-dependent signal changes was performed during this recognition task. Words were classified post hoc according to the subjects' responses, i.e. hits, false alarms, correct rejections and misses. Response-related fMRI-analysis was used to compare activation associated with the subjects' recognition success, i.e. signal intensities related to the presentation of words were compared by the above-mentioned four response types. RESULTS: During recognition, all word categories showed increased bilateral activation of the inferior frontal gyrus, the inferior temporal gyrus, the occipital lobe and the brainstem in comparison with the control condition. Hits and false alarms activated several areas including the left medial and lateral parieto-occipital cortex in comparison with subjectively unknown items, i.e. correct rejections and misses. Hits showed more pronounced activation in the medial, false alarms in the lateral parts of the left parieto-occipital cortex. CONCLUSIONS: Veridical and false recognition show common as well as different areas of cerebral activation in the left parieto-occipital lobe: increased activation of the medial parietal cortex by hits may correspond to true recognition, increased activation of the parieto-occipital cortex by false alarms may correspond to familiarity decisions. Further studies are needed to investigate the reasons for false decisions in healthy subjects and patients with memory problems.

Novelty detection and repetition suppression in a passive picture viewing task: a possible approach for the evaluation of neuropsychiatric disorders.

The applicability of functional magnetic resonance imaging (fMRI) in patients with Alzheimer's disease (AD) or schizophrenia is frequently limited by cognitive impairment, which prevents the adequate execution of complex tasks. An experimental design that puts only minor demands on the patients' cognitive ability but engages disease-relevant brain structures would be of benefit. Novelty detection and repetition suppression are two basic components of memory that might be used to investigate specific brain areas under these conditions. Novelty detection has been related to hippocampal activation increases. Stimulus repetition related activation decreases (suppression) have been observed in the extrastriate cortex and have been related to perceptual priming. Both processes have been examined primarily in neuroimaging studies with complex cognitive tasks. We used event-related fMRI to investigate novelty- and repetition-related effects in an attended but passive picture-viewing task in healthy subjects. The differential activation, detected in the novel vs. repeated contrast, was located in the bilateral anterior hippocampus and in bilateral occipital and inferior-temporal areas. The hippocampal activation is of interest because medial temporal lobe lesions are key features in AD and schizophrenia. The repetition-related activation decreases in the extrastriate areas are of potential value in investigating the conflicting results regarding perceptual priming impairment in both disorders. Our results indicate that activation of disease-relevant brain regions under passive task conditions is possible. This might increase the utility of functional imaging in cognitively impaired patients.