Yevhen Hlushchuk

Transient Suppression of Ipsilateral Primary Somatosensory Cortex during Tactile Finger Stimulation

The whole human primary somatosensory (SI) cortex is activated by contralateral tactile stimuli, whereas its subarea 2 displays neuronal responses also to ipsilateral stimuli. Here we report on a transient deactivation of area 3b of the ipsilateral SI during long-lasting tactile stimulation. We collected functional magnetic resonance imaging data with a 3 T scanner from 10 healthy adult subjects while tactile pulses were delivered at 1, 4, or 10 Hz in 25 s blocks to three right-hand fingers. In the contralateral SI cortex, activation [positive blood oxygenation level-dependent (BOLD) response] outlasted the stimulus blocks by 20 s, with an average duration of 45 s. In contrast, a transient deactivation (negative BOLD response) occurred in the ipsilateral rolandic cortex with an average duration of 18 s. Additional recordings on 10 subjects confirmed that the deactivation was not limited to the right SI but occurred in the SI cortex ipsilateral to the stimulated hand. Moreover, the primary motor cortex (MI) contained voxels that were phasically deactivated in response to both ipsilateral and contralateral touch. These data indicate that unilateral touch of fingers is associated, in addition to the well known activation of the contralateral SI cortex, with deactivation of the ipsilateral SI cortex and of the MI cortex of both hemispheres. The ipsilateral SI deactivation could result from transcallosal inhibition, whereas intracortical SI–MI connections could be responsible for the MI deactivation. The shorter time course of deactivation than activation would agree with stronger decay of inhibitory than EPSP at the applied stimulus repetition rates.

Aberrant temporal and spatial brain activity during rest in patients with chronic pain

In the absence of external stimuli, human hemodynamic brain activity displays slow intrinsic variations. To find out whether such fluctuations would be altered by persistent pain, we asked 10 patients with unrelenting chronic pain of different etiologies and 10 sex- and age-matched control subjects to rest with eyes open during 3-T functional MRI. Independent component analysis was used to identify functionally coupled brain networks. Time courses of an independent component comprising the insular cortices of both hemispheres showed stronger spectral power at 0.12 to 0.25 Hz in patients than in control subjects, with the largest difference at 0.16 Hz. A similar but weaker effect was seen in the anterior cingulate cortex, whereas activity of the precuneus and early visual cortex, used as a control site, did not differ between the groups. In the patient group, seed point-based correlation analysis revealed altered spatial connectivity between insulae and anterior cingulate cortex. The results imply both temporally and spatially aberrant activity of the affective pain-processing areas in patients suffering from chronic pain. The accentuated 0.12- to 0.25-Hz fluctuations in the patient group might be related to altered activity of the autonomic nervous system.

Enhancing the signal-to-noise ratio of ICA-based extracted ERPs

When decomposing single trial electroencephalography it is a challenge to incorporate prior physiological knowledge. Here, we develop a method that uses prior information about the phase-locking property of event-related potentials in a regularization framework to bias a blind source separation algorithm toward an improved separation of single-trial phase-locked responses in terms of an increased signal-to-noise ratio. In particular, we suggest a transformation of the data, using weighted average of the single trial and trial-averaged response, that redirects the focus of source separation methods onto the subspace of event-related potentials. The practical benefit with respect to an improved separation of such components from ongoing background activity and extraneous noise is first illustrated on artificial data and finally verified in a real-world application of extracting single-trial somatosensory evoked potentials from multichannel EEG-recordings.

Competing with peers: Mentalizing-related brain activity reflects what is at stake

Competition imposes constraints for humans who make decisions. Concomitantly, people do not only maximize their personal profit but they also try to punish unfair conspecifics. In bargaining games, subjects typically accept equal-share offers but reject unduly small offers; competition affects this balance. Here we used functional magnetic resonance imaging (fMRI) to study adjustment to competition in a bargaining game where subjects competed against another person for a share of the stake. For medium-sized, but not for minimum offers, competition increased the likelihood of acceptance and thus shifted behavior towards maximizing personal profits, emphasizing the importance of financial incentives. Specifically for medium-sized offers, competition was associated with increased brain activation bilaterally in the temporo-parietal junction, a region associated with mentalizing. In the right inferior frontal region, competition-related brain activation was strongest in subjects whose high acceptance rates in the standard ultimatum game hinted at a profit-oriented approach. The results suggest a network of brain areas supporting decision making under competition, with incentive-dependent mentalizing engaged when the competitors behavior is difficult to predict and when the stake is attractive enough to justify the effort.

What differs in visual recognition of handwritten vs. printed letters? An fMRI study.

In models of letter recognition, handwritten letters are considered as a particular font exemplar, not qualitatively different in their processing from printed letters. Yet, some data suggest that recognizing handwritten letters might rely on distinct processes, possibly related to motor knowledge. We applied functional magnetic resonance imaging to compare the neural correlates of perceiving handwritten letters vs. standard printed letters. Statistical analysis circumscribed to frontal brain regions involved in hand‐movement triggering and execution showed that processing of handwritten letters is supported by a stronger activation of the left primary motor cortex and the supplementary motor area. At the whole‐brain level, additional differences between handwritten and printed letters were observed in the right superior frontal, middle occipital, and parahippocampal gyri, and in the left inferior precentral and the fusiform gyri. The results are suggested to indicate embodiment of the visual perception of handwritten letters. Hum Brain Mapp, 2011.

Functional Subdivision of Group-ICA Results of fMRI Data Collected during Cinema Viewing

Independent component analysis (ICA) can unravel functional brain networks from functional magnetic resonance imaging (fMRI) data. The number of the estimated components affects both the spatial pattern of the identified networks and their time-course estimates. Here group-ICA was applied at four dimensionalities (10, 20, 40, and 58 components) to fMRI data collected from 15 subjects who viewed a 15-min silent film (“At land” by Maya Deren). We focused on the dorsal attention network, the default-mode network, and the sensorimotor network. The lowest dimensionalities demonstrated most prominent activity within the dorsal attention network, combined with the visual areas, and in the default-mode network; the sensorimotor network only appeared with ICA comprising at least 20 components. The results suggest that even very low-dimensional ICA can unravel the most prominent functionally-connected brain networks. However, increasing the number of components gives a more detailed picture and functionally feasible subdivision of the major networks. These results improve our understanding of the hierarchical subdivision of brain networks during viewing of a movie that provides continuous stimulation embedded in an attention-directing narrative.

Changes in brain function and morphology in patients with recurring herpes simplex virus infections and chronic pain.

ABSTRACT A recent study described for the first time a patient group that suffered from spontaneous chronic pain and from recurrent herpes simplex virus (HSV) infections. The patients had pain in widespread areas on one side of the body and were—due to subtle immunological abnormalities—susceptible to HSV infections. Although the clinical features of the pain suggested involvement of the central nervous system, supporting evidence for this was lacking. The objective of this study was to search for changes in the central nervous system that could account for the chronic pain in these patients. We monitored the central processing of pain and touch in eight patients and 11 healthy control subjects, who received painful heat and innocuous tactile stimuli to the hands during functional magnetic resonance imaging. Possible changes in the gray matter density of the brain were assessed with voxel‐based morphometry. We found functional changes in the patients’ central pain circuitry: activation to heat pain was weaker than in control subjects in the insular cortices, anterior cingulate cortex (ACC), and thalamus, while the activations to innocuous tactile stimuli were similar in both groups. Gray matter density was decreased in the patients’ frontal and prefrontal cortices and in the ACC. The observed functional and structural changes in the central pain circuitry, together with the clinical features of the chronic pain support the hypothesis for central involvement in the development of chronic pain in these patients.

Improved differentiation of tactile activations in human secondary somatosensory cortex and thalamus using cardiac-triggered fMRI

Functional magnetic resonance imaging (fMRI) can reveal human brain activations with high precision. The accuracy may, however, be impaired by movement and deformation of brain tissue associated with cardiac pulsations. Here we corrected for such artifacts by time-locking the fMRI data acquisition to the cardiac cycle in ten subjects who received tactile stimuli to their lips, fingers, and toes. The imaged brain areas covered the parietal operculum and the thalamus, including the secondary somatosensory cortex (SII) bilaterally. Variance of the blood-oxygen-level-dependent signal decreased on average by 38–40% in the SII cortex and by 26% in the thalamus during cardiac triggering compared with conventional imaging. Consequently, statistically significant responses were seen both in the SII cortex and in the ventroposterior thalamus in a larger number of subjects. At the cortical level, the activation pattern revealed two distinct representations for both fingers and toes in the SII region, and the more medial representations were detected with enhanced clarity during cardiac-triggered imaging. In the group-level analysis, the thalamic response to finger stimulation was seen with cardiac triggering, only.

Distal-to-proximal representation of volar index finger in human area 3b.

In area 3b of the monkey primary somatosensory cortex SI, the proximal phalanges of the fingers are represented close to the surface and the fingertips in the depth of the central sulcus. To study whether a similar arrangement might exist in humans, we applied tactile stimuli to the distal and proximal phalanges of the index finger in 11 healthy adults. Cortical somatosensory evoked fields were recorded with a whole-scalp neuromagnetometer. The sources of the responses were situated in the posterior wall of the central sulcus, statistically significantly more superior to proximal than distal stimuli, with a mean difference of 3.1 mm. Thus the distal-to-proximal representation of the index finger shows a similar order in human and monkey SI cortex.

Predicting stimulus-rate sensitivity of human somatosensory fMRI signals with MEG.

With increasing stimulus rate (SR), cortical EEG and MEG responses typically decrease in amplitude whereas BOLD fMRI signals increase. To address this discrepancy, we predicted BOLD responses with squared MEG waveforms using a recently proposed energy‐density model. Tactile stimuli were delivered to finger tips at SRs of 1, 4, or 10 Hz in successive 25‐s blocks, and brain signals were detected from area 3b of the primary somatosensory cortex of nine healthy adults using a 306‐channel whole‐scalp neuromagnetometer and a 3‐T fMRI magnet. The main MEG deflections decreased in amplitude as a function of SR, whereas the BOLD signals increased from 1‐ to 4‐Hz SR, with no further change at 10 Hz. MEG energy densities, obtained over the whole stimulus train and convolved with different hemodynamic response functions, predicted both the shape and amplitude of the BOLD signals well, and incorporation of nonlinear terms into the model did not offer any further advantage. Thus, squared MEG waveforms obtained over the entire stimulus train provided an appropriate estimate of area 3b neuronal activity associated with the BOLD signal. Hum Brain Mapp, 2009.