Stefan Elmer

Direct current induced short-term modulation of the left dorsolateral prefrontal cortex while learning auditory presented nouns.

BackgroundLittle is known about the contribution of transcranial direct current stimulation (tDCS) to the exploration of memory functions. The aim of the present study was to examine the behavioural effects of right or left-hemisphere frontal direct current delivery while committing to memory auditory presented nouns on short-term learning and subsequent long-term retrieval.MethodsTwenty subjects, divided into two groups, performed an episodic verbal memory task during anodal, cathodal and sham current application on the right or left dorsolateral prefrontal cortex (DLPFC).ResultsOur results imply that only cathodal tDCS elicits behavioural effects on verbal memory performance. In particular, left-sided application of cathodal tDCS impaired short-term verbal learning when compared to the baseline. We did not observe tDCS effects on long-term retrieval.ConclusionOur results imply that the left DLPFC is a crucial area involved in short-term verbal learning mechanisms. However, we found further support that direct current delivery with an intensity of 1.5 mA to the DLPFC during short-term learning does not disrupt longer lasting consolidation processes that are mainly known to be related to mesial temporal lobe areas. In the present study, we have shown that the tDCS technique has the potential to modulate short-term verbal learning mechanism.

Neurofunctional and Behavioral Correlates of Phonetic and Temporal Categorization in Musically Trained and Untrained Subjects

The perception of rapidly changing verbal and nonverbal auditory patterns is a fundamental prerequisite for speech and music processing. Previously, the left planum temporale (PT) has been consistently shown to support the discrimination of fast changing verbal and nonverbal sounds. Furthermore, it has been repeatedly shown that the functional and structural architecture of this supratemporal brain region differs as a function of musical training. In the present study, we used the functional magnetic resonance imaging technique, in a sample of professional musicians and nonmusicians, in order to examine the functional contribution of the left PT to the categorization of consonant-vowel syllables and their reduced-spectrum analogues. In line with our hypothesis, the musicians showed enhanced brain responses in the left PT and superior discrimination abilities in the reduced-spectrum condition. Moreover, we found a positive correlation between the responsiveness of the left PT and the performance in the reduced-spectrum condition across all subjects irrespective of musical expertise. These results have implications for our understanding of musical expertise in relation to segmental speech processing.

Increased cortical surface area of the left planum temporale in musicians facilitates the categorization of phonetic and temporal speech sounds

We measured musicians and non-musicians by using structural magnetic resonance imaging to investigate relationships between cortical features of the left planum temporale (PT) and the categorization of consonant-vowel (CV) syllables and their reduced-spectrum analogues. The present work is based on previous functional studies consistently showing that the left PT is particularly responsive to transient acoustic features in CV syllables and their reduced-spectrum analogues, and on striking evidence pointing to structural alterations of the left PT as a function of musicianship. By combining these two observations, we hypothesized to find that differences in cortical surface area (SA) and cortical thickness (CT) of the left PT in musicians may facilitate the categorization of fast-changing phonetic cues. Behavioural results indicated that musicians and non-musicians achieved a comparable performance in the categorization of CV syllables, whereas the musicians performed significantly better than the controls in the more demanding reduced-spectrum condition. This better behavioural performance corresponds to an increased cortical SA of the left PT in musicians compared to non-musicians. No differences in CT of the left PT were found between groups. In line with our predictions, we revealed a positive correlation between cortical SA of the left PT in musicians and the behavioural performance during the acoustically more demanding reduced-spectrum condition. Hence, we provide first evidence for a relationship between musical expertise, cortical SA of the left PT, and the processing of fast-changing phonetic cues.

Long-term exposure to music enhances the sensitivity of the auditory system in children

This event‐related brain potential study aims to contribute to the present debate regarding the effect of musical training on the maturation of the human auditory nervous system. To address this issue, we recorded the mismatch negativity (MMN) evoked by violin and pure sine‐wave tones in a group of 7.5‐ to 12‐year‐old children who had either several years of musical experience with Suzuki violin lessons, or no musical training. The strength of the MMN responses to violin tones evident in the Suzuki students clearly surpassed responses in controls; the reverse pattern was observed for sine‐wave tones. Suzuki students showed significantly shorter MMN latencies to violin tones than to pure tones; the MMN latency did not differ significantly between pure tones and violin sounds in the control group. Thus, our data provide general evidence of how and to what extent extensive musical experience affects the maturation of human auditory function at multiple levels, namely, accuracy and speed of auditory discrimination processing. Our findings add to the present understanding of neuroplastic organization and function of the mammalian nervous system. Furthermore, behavioural recordings obtained from the participating children provide corroborating evidence for a relationship between the duration and intensity of training, the specific sensitivity to instrumental timbre, and pitch recognition abilities.

Differential language expertise related to white matter architecture in regions subserving sensory‐motor coupling, articulation, and interhemispheric transfer

The technique of diffusion tensor imaging (DTI) has been used to investigate alterations in white matter architecture following long‐term training and expertise. Professional simultaneous interpreters (SI) provide an ideal model for the investigation of training‐induced plasticity due to the high demands placed on sound to motor mapping mechanisms, which are vital for executing fast interpretations. In line with our hypothesis, we found clusters with decreased fractional anisotropy (FA) in the SI group in brain regions previously shown to support sensory‐motor coupling mechanisms and speech articulation (cluster extent family‐wise error corrected, P < 0.01). Furthermore, we found an altered white matter architecture indicated by lower FA values in the SI group in the most anterior and posterior parts of the corpus callosum. Our results suggest that language expertise is accompanied by plastic adaptations in regions strongly involved in motor aspects of speech and in interhemispheric information transfer. These results have implications for our understanding of language expertise in relation to white matter adaptations. Hum Brain Mapp, 2011.

Processing demands upon cognitive, linguistic, and articulatory functions promote grey matter plasticity in the adult multilingual brain: Insights from simultaneous interpreters

Until now, considerable effort has been made to determine structural brain characteristics related to exceptional multilingual skills. However, at least one important question has not yet been satisfactorily addressed in the previous literature, namely whether and to which extent the processing demands upon cognitive, linguistic, and articulatory functions may promote grey matter plasticity in the adult multilingual brain. Based on the premise that simultaneous interpretation is a highly demanding linguistic task that places strong demands on executive and articulatory functions, here we compared grey matter volumes between professional simultaneous interpreters (SI) and multilingual control subjects. Thereby, we focused on a specific set of a-priori defined bilateral brain regions that have previously been shown to support neurocognitional aspects of language control and linguistic functions in the multilingual brain. These regions are the cingulate gyrus, caudate nucleus, frontal operculum (pars triangularis and opercularis), inferior parietal lobe (IPL) (supramarginal and angular gyrus), and the insula. As a main result, we found reduced grey matter volumes in professional SI, compared to multilingual controls, in the left middle-anterior cingulate gyrus, bilateral pars triangularis, left pars opercularis, bilateral middle part of the insula, and in the left supramarginal gyrus (SMG). Interestingly, grey matter volume in left pars triangularis, right pars opercularis, middle-anterior cingulate gyrus, and in the bilateral caudate nucleus was negatively correlated with the cumulative number of interpreting hours. Hence, we provide first evidence for an expertise-related grey matter architecture that may reflect a composite of brain characteristics that were still present before interpreting training and training-related changes.

Simultaneous interpreters as a model for neuronal adaptation in the domain of language processing

In the context of language processing, proficiency and age of acquisition have reliably been shown to have a strong influence on the functional and structural architecture of the human brain. The aim of the present EEG study was to examine the impact of language training as experienced by simultaneous interpreters (SI) on auditory word processing and to disentangle its influence from that of proficiency and age of acquisition. Eleven native German SI and controls matched in L2 proficiency and age of acquisition were asked to judge whether auditory presented disyllabic noun pairs both within and across the German (L1) and English (L2) languages were either semantically congruent or incongruent. We revealed enlarged N400 responses in SI while they detected incongruent trials both within the native (L1) and non-native (L2) language and also while they performed the task in the opposite direction as specifically trained (L1 to L2). These enlarged N400 responses in SI suggest a training-induced altered sensitivity to semantic processing within and across L1 and L2. The enlarged N400 responses we revealed in SI to congruent noun pairs during the German-English condition (L1 to L2) may indicate that SI could not benefit from an L1 prime when the target was a L2 word, suggesting additional processing resulting from long-term backwards (L2 to L1) training.

The “silent” imprint of musical training

Playing a musical instrument at a professional level is a complex multimodal task requiring information integration between different brain regions supporting auditory, somatosensory, motor, and cognitive functions. These kinds of task‐specific activations are known to have a profound influence on both the functional and structural architecture of the human brain. However, until now, it is widely unknown whether this specific imprint of musical practice can still be detected during rest when no musical instrument is used. Therefore, we applied high‐density electroencephalography and evaluated whole‐brain functional connectivity as well as small‐world topologies (i.e., node degree) during resting state in a sample of 15 professional musicians and 15 nonmusicians. As expected, musicians demonstrate increased intra‐ and interhemispheric functional connectivity between those brain regions that are typically involved in music perception and production, such as the auditory, the sensorimotor, and prefrontal cortex as well as Brocas area. In addition, mean connectivity within this specific network was positively related to musical skill and the total number of training hours. Thus, we conclude that musical training distinctively shapes intrinsic functional network characteristics in such a manner that its signature can still be detected during a task‐free condition. Hum Brain Mapp 37:536–546, 2016.

ERP differences of pre-lexical processing between dyslexic and non-dyslexic children

The present Event-Related Potential (ERP) study aimed to investigate group differences in the early processing stages of 36 dyslexic and 24 non-dyslexic 8-12 year old children performing a lexical decision (word/pseudoword judgment) task. Our data showed larger amplitudes of negative-going waveforms in non-dyslexic children than dyslexic children over occipital/occipitotemporal electrodes at about 220 ms after stimulus onset. This electrophysiological response has previously been identified in adult readers and labeled as the N170 component. Notably, as reflected by the topographic maps children irrespective of group processed the linguistic stimuli bilaterally and we did not observe any differences in ERP parameters in words and pseudowords within groups. Contrarily, behavioral responses indicate that words were more quickly recognized than pseudowords irrespective of group. By applying post-hoc ROI analyses based on a source estimation approach (sLORETA) we observed that non-dyslexic participants, when compared to dyslexic children, demonstrated significantly stronger current density over the left hemispheric inferior temporal lobe when processing pseudowords. We concluded that impaired reading is reflected by the decreased amplitude of the early lexical component N170. The lack of a left hemispheric processing preference in both groups and similar activation for words and pseudowords can be considered a lack of reading experience and less established reading system in children. Our results indicate that dyslexic children commit fewer specialized neuronal circuits for processing print and confirm the reasoning that acquiring reading skills requires cortical reorganization over occipitotemporal regions.

Musicianship boosts perceptual learning of pseudoword-chimeras: an electrophysiological approach.

A vast amount of previous work has consistently revealed that professional music training is associated with functional and structural alterations of auditory-related brain regions. Meanwhile, there is also an increasing array of evidence, which shows that musicianship facilitates segmental, as well as supra-segmental aspects of speech processing. Based on this evidence, we addressed a novel research question, namely whether professional music training has an influence on the perceptual learning of speech sounds. In the context of an EEG experiment, we presented auditory pseudoword-chimeras, manipulated in terms of spectral- or envelope-related acoustic information, to a group of professional musicians and non-musicians. During EEG measurements, participants were requested to assign the auditory-presented pseudoword-chimeras to one out of four visually presented templates. As expected, both groups showed behavioural learning effects during the time course of the experiment. These learning effects were associated with an increase in accuracy, a decrease in reaction time, as well as a decrease in the P2-like microstate duration in both groups. Notably, the musicians showed an increased learning performance compared to the controls during the first two runs of the spectral condition. This perceptual learning effect, which varies as a function of musical expertise, was reflected by a reduction of the P2-like microstate duration. Results may mirror transfer effects from musical training to the processing of spectral information in speech sounds. Hence, this study provides first evidence for a relationship between changes in microstates, musical expertise, and perceptual verbal learning mechanisms.