Faculty Bibliography

The left superior temporal cortex shows greater responsiveness to speech than to non-speech sounds according to previous neuroimaging studies, suggesting that this brain region has a special role in speech processing. However, since speech sounds differ acoustically from the non-speech sounds, it is possible that this region is not involved in speech perception per se, but rather in processing of some complex acoustic features. 'Sine wave speech' (SWS) provides a tool to study neural speech specificity using identical acoustic stimuli, which can be perceived either as speech or non-speech, depending on previous experience of the stimuli. We scanned 21 subjects using 3T functional MRI in two sessions, both including SWS and control stimuli. In the pre-training session, all subjects perceived the SWS stimuli as non-speech. In the post-training session, the identical stimuli were perceived as speech by 16 subjects. In these subjects, SWS stimuli elicited significantly stronger activity within the left posterior superior temporal sulcus (STSp) in the post- vs. pre-training session. In contrast, activity in this region was not enhanced after training in 5 subjects who did not perceive SWS stimuli as speech. Moreover, the control stimuli, which were always perceived as non-speech, elicited similar activity in this region in both sessions. Altogether, the present findings suggest that activation of the neural speech representations in the left STSp might be a pre-requisite for hearing sounds as speech

The development of neuroimaging methods has had a significant impact on the study of the human brain. Functional MRI, with its high spatial resolution, provides investigators with a method to localize the neuronal correlates of many sensory and cognitive processes. Magneto- and electroencephalography, in turn, offer excellent temporal resolution allowing the exact time course of neuronal processes to be investigated. Applying these methods to multisensory processing, many research laboratories have been successful in describing cross-sensory interactions and their spatiotemporal dynamics in the human brain. Here, we review data from selected neuroimaging investigations showing how vision can influence and interact with other senses, namely audition, touch, and olfaction. We highlight some of the similarities and differences in the cross-processing of the different sensory modalities and discuss how different neuroimaging methods can be applied to answer specific questions about multisensory processing. (journal abstract)

Understanding the conditions under which the brain integrates the different sensory streams and the mechanisms supporting this phenomenon is now a question at the forefront of neuroscience. In this paper, we discuss the opportunities for investigating these multisensory processes using modern imaging techniques, the nature of the information obtainable from each method and their benefits and limitations. Despite considerable variability in terms of paradigm design and analysis, some consistent findings are beginning to emerge. The detection of brain activity in human neuroimaging studies that resembles multisensory integration responses at the cellular level in other species, suggests similar crossmodal binding mechanisms may be operational in the human brain. These mechanisms appear to be distributed across distinct neuronal networks that vary depending on the nature of the shared information between different sensory cues. For example, differing extents of correspondence in time, space or content seem to reliably bias the involvement of different integrative networks which code for these cues. A combination of data obtained from haemodynamic and electromagnetic methods, which offer high spatial or temporal resolution respectively, are providing converging evidence of multisensory interactions at both 'early' and 'late' stages of processing--suggesting a cascade of synergistic processes operating in parallel at different levels of the cortex

Olfactory event-related potentials (OERP) have been used to investigate olfactory processing in health and disease. However, the reliability of the OERP has yet to be established statistically. The present study examined test-retest reliability of the OERP over a 4-week interval. EEG was recorded from Fz, Cz, and Pz, using a single-stimulus paradigm with amyl acetate. Reliabilities for ERP component latencies and interpeak amplitudes were assessed as intraclass and Pearson product-moment correlation coefficients. Reliabilities were higher for latency than for amplitude. Highest correlation coefficients were observed for P2 latency, specifically at Cz and Pz P3 amplitude and latency exhibited high reliability at Cz and Pz. Fz demonstrated weakest correlation coefficients. The data suggest that OERP reliability is comparable to that of auditory and visual ERPs, supporting the use of OERPs in both basic research and clinical assessment

Previous olfactory event-related potential (OERP) studies often employed the Velopharyngeal Closure (VC) method, which prevents respiratory air flow in the nose during odor presentation. However, the use of VC has limited the application of OERPs to populations able to perform this artificial breathing technique. The present study investigated the effects of Natural Breathing (NB) in comparison to VC on OERP latency and amplitude in young (mean age: 24 years) and elderly (mean age: 71 years) adults. OERPs were recorded from three midline scalp electrodes (Fz, Cz, Pz) for 15 trials in each breathing condition with an interstimulus interval of 3.5 min, using amyl-acetate as stimulus. Subjects were asked to report perceived stimulus intensity. A thermistor placed inside one nostril monitored nasal respiration and performance of VC. In the NB condition, subjects were instructed to breathe normally through mouth and nose, while stimulus presentation occurred during inspiration. In both breathing conditions, elderly subjects showed significantly smaller N1-P2 and N1-P3 interpeak amplitudes and longer latencies for N1, P2, P3 than younger subjects. VC generated significantly larger N1-P2 amplitudes across all electrode sites, whereas Natural Breathing produced a trend towards shorter P3 latencies. No significant interaction was found between age and breathing technique. The present investigation showed that the OERP is a sensitive measure for detecting age-related changes in olfactory function regardless of breathing technique