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

Impaired evoked and resting-state brain oscillations in patients with liver cirrhosis as revealed by magnetoencephalography

AbstractA number of studies suggest that the clinical manifestation of neurological deficits in hepatic encephalopathy results from pathologically synchronized neuronal oscillations and altered oscillatory coupling. In the present study spontaneous and evoked oscillatory brain activities were analyzed jointly with established behavioral measures of altered visual oscillatory processing. Critical flicker and fusion frequencies (CFF, FUF) were measured in 25 patients diagnosed with liver cirrhosis and 30 healthy controls. Magnetoencephalography (MEG) data were collected at rest and during a visual task employing repetitive stimulation. Resting MEG and evoked fields were analyzed. CFF and FUF were found to be reduced in patients, providing behavioral evidence for deficits in visual oscillatory processing. These alterations were found to be related to resting brain activity in patients, namely that the lower the dominant MEG frequency at rest, the lower the CFF and FUF. An analysis of evoked fields at sensor level indicated that in comparison to normal controls, patients were not able to dynamically adapt to flickering visual stimulation. Evoked activity was also analyzed based on independent components (ICs) derived by independent component analysis. The similarity between the shape of each IC and an artificial sine function representing the stimulation frequency was tested via magnitude squared coherence. In controls, we observed a small number of components that correlated strongly with the sine function and a high number of ICs that did not correlate with the sine function. Interestingly, patient data were characterized by a high number of moderately correlating components. Taken together, these results indicate a fundamental divergence of the cerebral resonance activity in cirrhotic patients

Attention modulates topology and dynamics of auditory sensory gating

This work challenges the widely accepted model of sensory gating as a preattention inhibitory process by investigating whether attention directed at the second tone (S2) within a paired‐click paradigm could affect gating at the cortical level. We utilized magnetoencephalography, magnetic resonance imaging and spatio‐temporal source localization to compare the cortical dynamics underlying gating responses across two conditions (passive and attention) in 19 healthy subjects. Source localization results reaffirmed the existence of a fast processing pathway between the prefrontal cortex (PFC) and bilateral superior temporal gyri (STG) that underlies the auditory gating process. STG source dynamics comprised two gating sub‐components, Mb1 and Mb2, both of which showed significant gating suppression (>51%). The attention directed to the S2 tone changed the gating network topology by switching the prefrontal generator from a dorsolateral location, which was active in the passive condition (18/19), to a medial location, active in the attention condition (19/19). Enhanced responses to the attended stimulus caused a significant reduction in gating suppression in both STG gating components (>50%). Our results demonstrate that attention not only modulates sensory gating dynamics, but also exerts topological rerouting of information processing within the PFC. The present data, suggesting that the cortical levels of early sensory processing are subject to top‐down influences, change the current view of gating as a purely automatic bottom‐up process

The Processing of Somatosensory Information shifts from an early parallel into a serial processing mode: a combined fMRI/MEG study.

The question regarding whether somatosensory inputs are processed in parallel or in series has not been clearly answered. Several studies that have applied dynamic causal modeling (DCM) to fMRI data have arrived at seemingly divergent conclusions. However, these divergent results could be explained by the hypothesis that the processing route of somatosensory information changes with time. Specifically, we suggest that somatosensory stimuli are processed in parallel only during the early stage, whereas the processing is later dominated by serial processing. This hypothesis was revisited in the present study based on fMRI analyses of tactile stimuli and the application of DCM to magnetoencephalographic (MEG) data collected during sustained (260 ms) tactile stimulation. Bayesian model comparisons were used to infer the processing stream. We demonstrated that the favored processing stream changes over time. We found that the neural activity elicited in the first 100 ms following somatosensory stimuli is best explained by models that support a parallel processing route, whereas a serial processing route is subsequently favored. These results suggest that the secondary somatosensory area (SII) receives information regarding a new stimulus in parallel with the primary somatosensory area (SI), whereas later processing in the SII is dominated by the preprocessed input from the SI

Abnormal Emotional Processing and Emotional Experience in Patients with Peripheral Facial Nerve Paralysis: An MEG Study

Abnormal emotional reactions of the brain in patients with facial nerve paralysis have not yet been reported. This study aims to investigate this issue by applying a machine-learning algorithm that discriminates brain emotional activities that belong either to patients with facial nerve paralysis or to healthy controls. Beyond this, we assess an emotion rating task to determine whether there are differences in their experience of emotions. MEG signals of 17 healthy controls and 16 patients with facial nerve paralysis were recorded in response to picture stimuli in three different emotional categories (pleasant, unpleasant, and neutral). The selected machine learning technique in this study was the logistic regression with LASSO regularization. We demonstrated significant classification performances in all three emotional categories. The best classification performance was achieved considering features based on event-related fields in response to the pleasant category, with an accuracy of 0.79 (95% CI (0.70, 0.82)). We also found that patients with facial nerve paralysis rated pleasant stimuli significantly more positively than healthy controls. Our results indicate that the inability to express facial expressions due to peripheral motor paralysis of the face might cause abnormal brain emotional processing and experience of particular emotions