Early Attentional Modulation of the Neural Network Evoked with the Auditory Paired-click Paradigm: An MEG Study

AbstractAlthough numerous research studies have explored the functional attributes of the human duration perception, the spatio- temporal information on cortical networks underlying this process is still an open question. Moreover, the issue of possible differences in the nature of timing mechanisms responsible for perception of sub- and supra-second intervals requires the implementation of the functional brain imaging techniques with both high spatial and temporal resolution. Attention is very frequently used as a modulating factor for the perceived duration of a sensory stimulus. The non-attended stimuli appear to last shorter than the attended ones, increasing the perceived duration of a concurrent stimulus (Gorea, 2011). This study challenges the accepted model of early sensory responses, activated during the first 100ms after stimulus presentation, as preattentive, automatic processes which modulate the neural sensitivity to incoming stimuli (gating phenomena). We utilized Elekta Neuromag 306-channel whole-head system for magnetoencephalography (MEG) measurements and multi-dipole Calibrated Start Spatio Temporal (CSST) localization technique (Ranken et al., 2002) to investigate whether voluntary attention directed at the second tone of a pair in the standard paired-click paradigm could affect cortical networks underlying the gating out phenomenon. MEG recordings were obtained in a magnetically shielded room at the Biomagnetic Center in Jena, Germany. Two consecutive (ISI=500ms) identical short tonnes (S1 and S2; duration=20ms; f=1200Hz; ITI=8±1s) were used to evoke standard gating cortical responses in 19 healthy participants (21-38 years). In the second condition, the task was to direct attention toward the second tone and to respond to a rarely presented non-identical second tone of the pair (R=1300Hz, p(S1R)=0.3). MEG recordings showed transient early and middle latency responses with peak amplitudes over the temporo-parietal sensors followed by a peak of a sustained activity. Less prominent transient activity was recorded over the frontal sensors, accompanied with a more steady- state component from 100 until 400ms post-stimulus for both conditions. Preliminary results of the CSST spatio-temporal analyses revealed 4-6 brain regions activated during 20-500ms time interval including bilateral superior temporal gyrus (STG), bilateral and medial prefrontal (PF), bilateral parietal (PA) regions, and central motor cortex area. A cortical source underlying the steady-state component was identified in the left prefrontal region for S1 tone, and in central posterior regions (PA) for the repeated tone S2. During the standard paradigm the M50 gating suppression was observed only for bilateral STG sources while bilateral PF and PA sources did not show any reduction in the response during the first 100ms post-stimulus. Targeting the attention towards the second tone enhanced the M50 amplitude of the bilateral STG responses in respect to the repeated stimulus S2 and caused a change in the activated network evident by the emergence of a new generator in the medial PF area (orbitofrontal) instead of dorsolateral PF generators evoked in non-attended condition. These results demonstrate that voluntary attention can exert a topological and functional modulatory influence on the neural network even during early stages of auditory processing

Semiempirical vs. Ab Initio Calculations of Molecular Properties. Part 3. Electric Field Gradients at 14N Nuclei in some Small Molecules

Electric field gradients (EFG) at nitrogen nuclei in some small and medium size molecules are calculated by the semiempirical CND0/2D and SCC-MO methods. A salient feature of our procedure is accurate evaluation of matrix elements ot the EFG operator. Hence, comparison of EFG values with the results or more sophisticated ab initio procedures obtained by suitable basis sets indicates flaws and shortcomings of the semiempirical schemes

EEG/MEG Source Imaging: Methods, Challenges, and Open Issues

We present the four key areas of research—preprocessing, the volume conductor, the forward problem, and the inverse problem—that affect the performance of EEG and MEG source imaging. In each key area we identify prominent approaches and methodologies that have open issues warranting further investigation within the community, challenges associated with certain techniques, and algorithms necessitating clarification of their implications. More than providing definitive answers we aim to identify important open issues in the quest of source localization

Insights on the Neuromagnetic Representation of Temporal Asymmetry in Human Auditory Cortex.

Communication sounds are typically asymmetric in time and human listeners are highly sensitive to this short-term temporal asymmetry. Nevertheless, causal neurophysiological correlates of auditory perceptual asymmetry remain largely elusive to our current analyses and models. Auditory modelling and animal electrophysiological recordings suggest that perceptual asymmetry results from the presence of multiple time scales of temporal integration, central to the auditory periphery. To test this hypothesis we recorded auditory evoked fields (AEF) elicited by asymmetric sounds in humans. We found a strong correlation between perceived tonal salience of ramped and damped sinusoids and the AEFs, as quantified by the amplitude of the N100m dynamics. The N100m amplitude increased with stimulus half-life time, showing a maximum difference between the ramped and damped stimulus for a modulation half-life time of 4 ms which is greatly reduced at 0.5 ms and 32 ms. This behaviour of the N100m closely parallels psychophysical data in a manner that: i) longer half-life times are associated with a stronger tonal percept, and ii) perceptual differences between damped and ramped are maximal at 4 ms half-life time. Interestingly, differences in evoked fields were significantly stronger in the right hemisphere, indicating some degree of hemispheric specialisation. Furthermore, the N100m magnitude was successfully explained by a pitch perception model using multiple scales of temporal integration of auditory nerve activity patterns. This striking correlation between AEFs, perception, and model predictions suggests that the physiological mechanisms involved in the processing of pitch evoked by temporal asymmetric sounds are reflected in the N100m

Magnetoencephalography: from signals to dynamic cortical networks

"Magnetoencephalography (MEG) provides a time-accurate view into human brain function. The concerted action of neurons generates minute magnetic fields that can be detected---totally noninvasively---by sensitive multichannel magnetometers. The obtained millisecond accuracycomplements information obtained by other modern brain-imaging tools. Accurate timing is quintessential in normal brain function, often distorted in brain disorders. The noninvasiveness and time-sensitivityof MEG are great assets to developmental studies, as well. This multiauthored book covers an ambitiously wide range of MEG research from introductory to advanced level, from sensors to signals, and from focal sources to the dynamics of cortical networks. Written by active practioners of this multidisciplinary field, the book contains tutorials for newcomers and chapters of new challenging methods and emerging technologies to advanced MEG users. The reader will obtain a firm grasp of the possibilities of MEG in the study of audition, vision, somatosensation, sensorimotor integration, pain, and cognitive functions both in healthy subjects and several neurological and psychiatric disorders. Development is covered from fetal and pediatric studies to the effects of aging. This volume brings fresh and welcome diversity to the existing MEG literature." MEG book review by Riitta Hari, Academician of Science, Aalto Universit

MEG study on temporal asymmetry processing in the human auditory cortex

cote interne IRCAM: Kult03fNone / NoneNational audienceNon

High-resolution EEG analysis of power spectral density maps and coherence networks in a proportional reasoning task

Proportional reasoning is very important logical skill required in mathematics and science problem solving as well as in everyday life decisions. However, there is a lack of studies on neurophysiological correlates of proportional reasoning. To explore the brain activity of healthy adults while performing a balance scale task, we used high-resolution EEG techniques and graph-theory based connectivity analysis. After unskilled subjects learned how to properly solve the task, their cortical power spectral density (PSD) maps revealed an increased parietal activity in the beta band. This indicated that subjects started to perform calculations. In addition, the number of inter-hemispheric connections decreased after learning, implying a rearrangement of the brain activity. Repeated performance of the task led to the PSD decrease in the beta and gamma bands among parietal and frontal regions along with a synchronization of lower frequencies. These findings suggest that repetition led to a more automatic task performance. Subjects were also divided in two groups according to their scores on the test of logical thinking (TOLT). Although no group differences in the accuracy and reaction times were found, EEG data showed higher activity in the beta and gamma bands for the group that scored better on TOLT. Learning and repetition induced changes in the pattern of functional connectivity were evident for all frequency bands. Overall, the results indicated that higher frequency oscillations in frontal and parietal regions are particularly important for proportional reasoning. © 2012 Springer Science+Business Media New York

High-resolution EEG analysis of power spectral density maps and coherence networks in a proportional reasoning task.

International audienceProportional reasoning is very important logical skill required in mathematics and science problem solving as well as in everyday life decisions. However, there is a lack of studies on neurophysiological correlates of proportional reasoning. To explore the brain activity of healthy adults while performing a balance scale task, we used high-resolution EEG techniques and graph-theory based connectivity analysis. After unskilled subjects learned how to properly solve the task, their cortical power spectral density (PSD) maps revealed an increased parietal activity in the beta band. This indicated that subjects started to perform calculations. In addition, the number of inter-hemispheric connections decreased after learning, implying a rearrangement of the brain activity. Repeated performance of the task led to the PSD decrease in the beta and gamma bands among parietal and frontal regions along with a synchronization of lower frequencies. These findings suggest that repetition led to a more automatic task performance. Subjects were also divided in two groups according to their scores on the test of logical thinking (TOLT). Although no group differences in the accuracy and reaction times were found, EEG data showed higher activity in the beta and gamma bands for the group that scored better on TOLT. Learning and repetition induced changes in the pattern of functional connectivity were evident for all frequency bands. Overall, the results indicated that higher frequency oscillations in frontal and parietal regions are particularly important for proportional reasoning

Schematic diagram of the Auditory Image Model and the Top-down Modulated Hierarchical Model of Pitch.

<p>a) Schematic view of the Auditory Image Model (AIM) [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0153947#pone.0153947.ref014" target="_blank">14</a>]. In the first stage, peripheral auditory filters transform the input waveform into a multi-channel representation of basilar membrane motion. The next stage applies a hair cell model and converts this motion into a neural activity pattern in the auditory nerve (NAP). In the final stage, this signal is used to produce a stabilised representation of the stimuli by means of strobed temporal integration. The output of this process is termed the stabilised auditory image (SAI) of the input stimulus. b) Schematic view of the top-down modulated Hierarchical Generative Model of pitch perception (GPM) [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0153947#pone.0153947.ref017" target="_blank">17</a>]. The peripheral processing is similar to the one in AIM (bottom). The next step consists of a coincidence detection process of auditory nerve activity patterns for different cochlear delay lines <i>l</i>, <i>A</i>₁(<i>t</i>, <i>l</i>). Further processing is carried out by two consecutive ensemble models <i>A</i>₂ and <i>A</i>₃ performing leaky integrations of input activity using time-varying integration windows. Such ensembles correspond putatively to pre-thalamic and central auditory areas. A top-down, stimulus-dependent mechanism modulates the size of the effective integration windows of bottom-up information.</p