Alfredo Brancucci

Inhibition of auditory cortical responses to ipsilateral stimuli during dichotic listening: evidence from magnetoencephalography

The present magnetoencephalography (MEG) study on auditory evoked magnetic fields (AEFs) was aimed at verifying whether during dichotic listening the contralateral auditory pathway inhibits the ipsilateral one, as suggested by behavioural and patient studies. Ten healthy subjects were given a randomized series of three complex tones (261, 293 and 391 Hz, 500 ms duration), which were delivered monotically and dichotically with different intensities [60, 70 or 80 dBA (audio decibels)]. MEG data were recorded from the right auditory cortex. Results showed that the M100 amplitude over the right auditory cortex increased progressively when tones of increasing intensity were provided at the ipsilateral (right) ear. This effect on M100 was abolished when a concurrent tone of constant intensity was delivered dichotically at the contralateral (left) ear, suggesting that the contralateral pathway inhibited the ipsilateral one. The ipsilateral inhibition was present only when the contralateral tone fundamental frequency was similar to the ipsilateral tone. It was proposed that the occlusion mechanism would be exerted in cortical auditory areas as the dichotic effects were observed at M100 but not M50 component. This is the first evidence showing a neurophysiological inhibition driven by the contralateral auditory pathway over the ipsilateral one during dichotic listening.

Anticipatory cortical responses during the expectancy of a predictable painful stimulation. A high-resolution electroencephalography study.

In the present study, high‐resolution electroencephalography techniques modelled the spatiotemporal pattern of human anticipatory cortical responses preceding expected galvanic painful stimuli (non‐painful stimuli as a control). Do these responses reflect the activation of associative other than somatosensory systems? Anticipatory processes were probed by alpha oscillations (6–12 Hz) for the evaluation of thalamocortical channels and by negative event‐related potentials for the evaluation of cortical excitability. Compared with the control condition, a progressive reduction of the alpha power was recognized over the primary somatosensory cortex from 2 s before the painful stimulation. In contrast, the anticipatory event‐related potentials were negligible during the expectancy period. The results on the alpha power suggest that the expectancy of the painful stimulation specifically facilitated the somatosensory thalamocortical channel. Remarkably, the associative frontal‐parietal areas were not involved, possibly due to the predictable and repetitive features of the painful stimulus. The present results also suggest that negative event‐related potentials are modest preceding warned stimuli (even if painful) with a simple information content.

Effects of Transcranial Direct Current Stimulation on episodic memory related to emotional visual stimuli.

The present study investigated emotional memory following bilateral transcranial electrical stimulation (direct current of 1 mA, for 20 minutes) over fronto-temporal cortical areas of healthy participants during the encoding of images that differed in affective arousal and valence. The main result was a significant interaction between the side of anodal stimulation and image emotional valence. Specifically, right anodal/left cathodal stimulation selectively facilitated the recall of pleasant images with respect to both unpleasant and neutral images whereas left anodal/right cathodal stimulation selectively facilitated the recall of unpleasant images with respect to both pleasant and neutral images. From a theoretical perspective, this double dissociation between the side of anodal stimulation and the advantage in the memory performance for a specific type of stimulus depending on its pleasantness supported the specific-valence hypothesis of emotional processes, which assumes a specialization of the right hemisphere in processing unpleasant stimuli and a specialization of the left hemisphere in processing pleasant stimuli. From a methodological point of view, first we found tDCS effects strictly dependent on the stimulus category, and second a pattern of results in line with an interfering and inhibitory account of anodal stimulation on memory performance. These findings need to be carefully considered in applied contexts, such as the rehabilitation of altered emotional processing or eye-witness memory, and deserve to be further investigated in order to understand their underlying mechanisms of action.

Asymmetries of the human social brain in the visual, auditory and chemical modalities

Structural and functional asymmetries are present in many regions of the human brain responsible for motor control, sensory and cognitive functions and communication. Here, we focus on hemispheric asymmetries underlying the domain of social perception, broadly conceived as the analysis of information about other individuals based on acoustic, visual and chemical signals. By means of these cues the brain establishes the border between ‘self’ and ‘other’, and interprets the surrounding social world in terms of the physical and behavioural characteristics of conspecifics essential for impression formation and for creating bonds and relationships. We show that, considered from the standpoint of single- and multi-modal sensory analysis, the neural substrates of the perception of voices, faces, gestures, smells and pheromones, as evidenced by modern neuroimaging techniques, are characterized by a general pattern of right-hemispheric functional asymmetry that might benefit from other aspects of hemispheric lateralization rather than constituting a true specialization for social information.

Attentional processes and cognitive performance during expectancy of painful galvanic stimulations: a high-resolution EEG study

In the present high-resolution electroencephalographic (EEG) study, an omitted-stimulus paradigm induced a strong expectancy for a predictable painful stimulation (nonpainful in the control condition). During the expectancy of pain, concurrent cognitive demands were superimposed. The aim was to investigate the effects on primary sensorimotor and central midline areas of the competition among concurrent attentional processes related to cognition and pain expectancy, as indexed by behavioral performance and EEG data. A main issue was whether cognitive performance decreases, due to a re-allocation of attentional resources on primary sensorimotor and midline areas for the anticipation of pain. Behavioral results showed no differences in the cognitive (working memory) performance during the expectancy of nonpainful versus painful stimulations. In parallel, anticipatory event-related potentials (ERPs) were negligible in line with a low emotional reactivity/alertness as revealed by heart rate deceleration (HRD), skin conductance response (SCR), and low-band (6-10Hz) alpha EEG oscillations. In contrast, high-band alpha EEG oscillations (10-12Hz) over the contralateral primary sensorimotor cortex decreased more during the expectancy of painful compared to nonpainful stimuli, in line with an increased anticipatory preparation of the somatosensory channel. These findings provide further evidence on the fact that attentional processes at the basis of cognition can be defended by the anticipation of pain, at least when the incoming painful stimuli are repetitive and predictable. This happens even if the brain increases preparatory processes of the specific sensory channel to be targeted by the painful stimulus.

Laterality in the perception of temporal cues of musical timbre

Laterality in the perception of non-stationary aspects of musical timbre was investigated in 54 right-handed non-musicians. Timbre differences were produced by altering the amplitude envelope of a steady-state complex tone. Two single-choice tests with attention directed to one ear were used--a dichotic test and a monaural test with contralateral white noise. Dependent variables were reaction time and accuracy. Both tests showed a significant left ear advantage for reaction time. For the accuracy variable, a significant left ear advantage was found only in the monaural test. Results are briefly discussed in terms of their compatibility with the generally accepted notion that spectral and temporal integrations of sounds are primarily functions of the right and left hemisphere, respectively.

Right hemisphere specialization for intensity discrimination of musical and speech sounds

Sound intensity is the primary and most elementary feature of auditory signals. Its discrimination plays a fundamental role in different behaviours related to auditory perception such as sound source localization, motion detection, and recognition of speech sounds. This study was aimed at investigating hemispheric asymmetries for processing intensity of complex tones and consonant-vowel syllables. Forty-four right-handed non-musicians were presented with two dichotic matching-to-sample tests with focused attention: one with complex tones of different intensities (musical test) and the other with consonant-vowel syllables of different intensities (speech test). Intensity differences (60, 70, and 80 dBA) were obtained by altering the gain of a synthesized harmonic tone (260 Hz fundamental frequency) and of a consonant-vowel syllable (/ba/) recorded from a natural voice. Dependent variables were accuracy and reaction time. Results showed a significant clear-cut left ear advantage in both tests for both dependent variables. A monaural control experiment ruled out possible attentional biases. This study provides behavioural evidence of a right hemisphere specialization for the perception of the intensity of musical and speech sounds in healthy subjects.

Alpha event-related desynchronization preceding a go/no-go task: a high-resolution EEG study.

The authors delineated the time evolution of alpha event-related desynchronization over human frontal, parietal, and primary sensorimotor areas during the expectancy of a go/no-go task. The main issue under investigation was whether anticipatory processes impinged upon cortical areas in sequential or parallel mode. Compared with the control condition, in the experimental condition there was an Alpha 1 desynchronization over the central midline, an Alpha 2 desynchronization increasing over primary sensorimotor areas, and an Alpha 3 desynchronization increasing in parallel over bilateral primary sensorimotor areas. These processes had different temporal features. Results disclose an anticipatory activity of central midline areas and primary sensorimotor areas in both parallel and sequential modes. This reflects an adaptive, energy-consuming strategy rather than an economic waiting for the go stimulus.

Left hemisphere specialization for duration discrimination of musical and speech sounds

Hemispheric asymmetries for processing duration of non-verbal and verbal sounds were investigated in 60 right-handed subjects. Two dichotic tests with attention directed to one ear were used, one with complex tones and one with consonant-vowel syllables. Stimuli had three possible durations: 350, 500, and 650 ms. Subjects judged whether the duration of a probe was same or different compared to the duration of the target presented before it. Target and probe were part of two dichotic pairs presented with 1s interstimulus interval and occurred on the same side. Dependent variables were reaction time and accuracy. Results showed a significant right ear advantage for both dependent variables with both complex tones and consonant-vowel syllables. This study provides behavioural evidence of a left hemisphere specialization for duration perception of both musical and speech sounds in line with the current view based on a parameter--rather than domain-specific structuring of hemispheric perceptual asymmetries.

Expectancy of pain is influenced by motor preparation: a high-resolution EEG study of cortical alpha rhythms

This high-resolution electroencephalographic (EEG) study on alpha event-related desynchronization (ERD) evaluated whether anticipatory activity precedes a sensorimotor interaction induced by concomitant painful stimuli and sensorimotor demand. An omitted-stimulus paradigm induced the expectancy of the painful stimulation at the left hand. In the experimental condition, the painful stimulation was associated with a visual go/no-go task triggering right-hand movements. Two control conditions manipulated the painful sensorimotor interaction variable. Compared with the control conditions, the expectancy of the painful sensorimotor interaction increased the high-band alpha EEG oscillations over the right primary sensorimotor cortex contralateral to the nociceptive stimuli and, to a lesser extent, over the centroparietal midline. These findings suggest that concomitant painful stimuli and simple sensorimotor go/no-go demands affect anticipatory activity as revealed by alpha ERD.