When EMG contamination does not necessarily hide high-frequency EEG: scalp electrical recordings before and after Dysport injections.

The main aim of the present study was to investigate effects of partial reductions of electromyogram (EMG) on high-frequency scalp electroencephalogram (EEG) at rest and during performance of certain cognitive tasks. Nineteen healthy women performed the same cognitive tasks before and after cosmetic injections of Dysport in certain sites of facial muscles. Scalp EEG and EMG were recorded. Impact of Dysport injections on changes of spectral power in ß2 and low γ frequency ranges (18-40 Hz) in EEG and EMG derivations was investigated. Also changes of spectral power in EEG and EMG derivations during comparisons of different cognitive states were calculated before and after Dysport injections separately. Dysport injections led to EMG decreases in facial muscles around the injection zones and also led to reductions of power of electric processes in scalp derivations. Along with it results of EEG power comparisons between the pairs of the cognitive states were qualitatively similar before and after Dysport injections. These facts to all appearance demonstrate that though scalp EEGs in the range above 15-40 Hz are contaminated by EMG, in certain experimental situations EMG contamination does not preclude qualitative detections of electroencephalographic correlates of mental activities in ß2 and low γ frequency ranges. Parallel EEG and EMG registrations can help not to overestimate EMG contamination in psychophysiological EEG studies.

Changes in functional connectivity within the fronto-temporal brain network induced by regular and irregular Russian verb production.

Functional connectivity between brain areas involved in the processing of complex language forms remains largely unexplored. Contributing to the debate about neural mechanisms underlying regular and irregular inflectional morphology processing in the mental lexicon, we conducted an fMRI experiment in which participants generated forms from different types of Russian verbs and nouns as well as from nonce stimuli. The data were subjected to a whole brain voxel-wise analysis of context dependent changes in functional connectivity [the so-called psychophysiological interaction (PPI) analysis]. Unlike previously reported subtractive results that reveal functional segregation between brain areas, PPI provides complementary information showing how these areas are functionally integrated in a particular task. To date, PPI evidence on inflectional morphology has been scarce and only available for inflectionally impoverished English verbs in a same-different judgment task. Using PPI here in conjunction with a production task in an inflectionally rich language, we found that functional connectivity between the left inferior frontal gyrus (LIFG) and bilateral superior temporal gyri (STG) was significantly greater for regular real verbs than for irregular ones. Furthermore, we observed a significant positive covariance between the number of mistakes in irregular real verb trials and the increase in functional connectivity between the LIFG and the right anterior cingulate cortex in these trails, as compared to regular ones. Our results therefore allow for dissociation between regularity and processing difficulty effects. These results, on the one hand, shed new light on the functional interplay within the LIFG-bilateral STG language-related network and, on the other hand, call for partial reconsideration of some of the previous findings while stressing the role of functional temporo-frontal connectivity in complex morphological processes.

An ER-fMRI study of Russian inflectional morphology.

The generation of regular and irregular past tense verbs has long been a testing ground for different models of inflection in the mental lexicon. Behavioral studies examined a variety of languages, but neuroimaging studies rely almost exclusively on English and German data. In our fMRI experiment, participants inflected Russian verbs and nouns of different types and corresponding nonce stimuli. Irregular real and nonce verbs activated inferior frontal and inferior parietal regions more than regular verbs did, while no areas were more activated in the opposite comparison. We explain this activation pattern by increasing processing load: a parametric contrast revealed that these regions are also more activated for nonce stimuli compared to real stimuli. A very similar pattern is found for nouns. Unlike most previously obtained results, our findings are more readily compatible with the single-system approach to inflection, which does not postulate a categorical difference between regular and irregular forms.

Attention-related modulation of auditory-cortex responses to speech sounds during dichotic listening.

Event-related magnetic fields (ERFs) were measured with magnetoencephalography (MEG) in fifteen healthy right-handed participants listening to sequences of consonant-vowel syllable pairs delivered dichotically (one syllable presented to the left ear and another syllable simultaneously to the right ear). The participants were instructed to press a response button to occurrences of a particular target syllable. In a condition with no other instruction (the non-forced condition, NF), they showed the well-known right-ear advantage (REA), that is, the participants responded more often to target syllables delivered to the right ear than to targets delivered to the left ear. The same was true in the forced-right (FR) condition, where the participants were instructed to attend selectively to the right-ear syllables and respond only to targets among them. In the forced-left (FL) condition, where they were instructed to respond only to left-ear targets, they responded more often to targets in this ear than to targets in the right ear. At 300-500 ms from syllable pair onset, a sustained field (SF) in ERFs to the syllable pairs was stronger in the left auditory cortex than in the right auditory cortex in the NF and FR conditions, while the opposite was true in the FL condition. Thus selective attention during dichotic listening leads to stronger processing of speech sounds in the auditory cortex contralateral to the attended direction. Our results also suggest that the REA observed for dichotic speech may involve a bias of attention to the right side even when there is no instruction to do so. This supports Kinsbourne's (1970) model of attention bias as a general principle of laterality.

Selective attention to human voice enhances brain activity bilaterally in the superior temporal sulcus.

Regional cerebral blood flow was measured with positron emission tomography (PET) in 10 healthy male volunteers. They heard two binaurally delivered concurrent stories, one spoken by a male voice and the other by a female voice. A third story was presented at the same time as a text running on a screen. The subjects were instructed to attend silently to one of the stories at a time. In an additional resting condition, no stories were delivered. PET data showed that in comparison with the reading condition, the brain activity in the speech-listening conditions was enhanced bilaterally in the anterior superior temporal sulcus including cortical areas that have been reported to be specifically sensitive to human voice. Previous studies on attention to non-linguistic sounds and visual objects, in turn, showed prefrontal activations that are presumably related to attentional control functions. However, comparisons of the present speech-listening and reading conditions with each other or with the resting condition indicated no prefrontal activity, except for an activation in the inferior frontal cortex that was presumably associated with semantic and syntactic processing of the attended story. Thus, speech listening, as well as reading, even in a distracting environment appears to depend less on the prefrontal control functions than do other types of attention-demanding tasks, probably because selective attention to speech and written text are over-learned actions rehearsed daily.

Linguistic processing in visual and modality-nonspecific brain areas: PET recordings during selective attention.

Positron emission tomography (PET) was used to investigate the neural basis of selective processing of linguistic material during concurrent presentation of multiple stimulus streams ("cocktail-party effect"). Fifteen healthy right-handed adult males were to attend to one of three simultaneously presented messages: one presented visually, one to the left ear, and one to the right ear. During the control condition, subjects attended to visually presented consonant letter strings and ignored auditory messages. This paper reports the modality-nonspecific language processing and visual word-form processing, whereas the auditory attention effects have been reported elsewhere [Cogn. Brain Res. 17 (2003) 201]. The left-hemisphere areas activated by both the selective processing of text and speech were as follows: the inferior prefrontal (Brodmann's area, BA 45, 47), anterior temporal (BA 38), posterior insular (BA 13), inferior (BA 20) and middle temporal (BA 21), occipital (BA 18/30) cortices, the caudate nucleus, and the amygdala. In addition, bilateral activations were observed in the medial occipito-temporal cortex and the cerebellum. Decreases of activation during both text and speech processing were found in the parietal (BA 7, 40), frontal (BA 6, 8, 44) and occipito-temporal (BA 37) regions of the right hemisphere. Furthermore, the present data suggest that the left occipito-temporal cortex (BA 18, 20, 37, 21) can be subdivided into three functionally distinct regions in the posterior-anterior direction on the basis of their activation during attentive processing of sublexical orthography, visual word form, and supramodal higher-level aspects of language.

Hemispheric lateralization of cerebral blood-flow changes during selective listening to dichotically presented continuous speech.

Regional cerebral blood flow (rCBF) was measured with positron emission tomography (PET) while subjects were selectively listening to continuous speech delivered to one ear and ignoring concurrent speech delivered to the opposite ear, as well as concurrent text or letter strings running on a screen. rCBF patterns associated with selective listening either to the left-ear or right-ear speech message were compared with each other and with rCBF patterns in two visual-attention conditions in which the subjects ignored both speech messages and either read the text or discriminated the meaningless letter strings moving on the screen. Attention to either speech message was associated with enhanced activity in the superior temporal cortex of the language-dominant left hemisphere, as well as in the superior and middle temporal cortex of the right hemisphere suggesting enhanced processing of prosodic features in the attended speech. Moreover, enhanced activity during attention to either speech message was observed in the right parietal areas known to have an important role in directing spatial attention. Evidence was also found for attentional tuning of the left and right auditory cortices to select information from the contralateral auditory hemispace.