Neuromagnetic steady-state responses to auditory stimuli

Steady‐state magnetic responses to clicks presented at rates between 10 and 70 Hz have been recorded in healthy humans. The responses were highest in amplitude around 40 Hz. This amplitude enhancement is satisfactorily explained by summation of responses evoked by single clicks. The field maps suggest activation of the auditory cortex at all stimulus frequencies. Similar responses were obtained with gated noise bursts and by pauses in a series of clicks. The mean "apparent latency", determined from the phase lag at rates 30–70 Hz, was 54 ms. The physiological relevance of this quantity is shown to be questionable.Peer reviewe

Auditory Cortical Responses to Speech-Like Stimuli in Dyslexic Adults

Auditory cortical processing of speech-like sounds was studied in 9 dyslexic and 11 normal-reading adults. Noise/ square-wave sequences, mimicking transitions from a fricative consonant to a vowel, were presented binaurally once every 1.1 sec and the cortical responses were recorded with a whole-scalp neuromagnetometer. The auditory cortices of both hemispheres were less reactive to acoustical changes in dyslexics than in controls, as was evident from the weaker responses to the noise/square-wave transitions. The results demonstrate that dyslexic adults are deficient in processing acoustic changes presented in rapid succession within tens to hundreds of milliseconds. The observed differences could be related to insufficient triggering of automatic auditory attention, resulting, for instance, from a general deficiency of the magnocellular system.Peer reviewe

Modulation of Rolandic Beta-Band Oscillations during Motor Simulation of Joint Actions

Successful joint actions require precise temporal and spatial coordination between individuals who aim to achieve a common goal. A growing number of behavioral data suggest that to efficiently couple and coordinate a joint task, the actors have to represent both own and the partner’s actions. However it is unclear how the motor system is specifically recruited for joint actions. To find out how the goal and the presence of the partner’s hand can impact the motor activity during joint action, we assessed the functional state of 16 participants’ motor cortex during observation and associated motor imagery of joint actions, individual actions, and non-goal-directed actions performed with either 1 or 2 hands. As an indicator of the functional state of the motor cortex, we used the reactivity of the rolandic magnetoencephalographic (MEG) beta rhythm following median-nerve stimulation. Motor imagery combined with action observation was associated with activation of the observer’s motor cortex, mainly in the hemisphere contralateral to the viewed (and at the same time imagined) hand actions. The motor-cortex involvement was enhanced when the goal of the actions was visible but also, in the ipsilateral hemisphere, when the partner’s hand was visible in the display. During joint action, the partner’s action, in addition to the participant’s own action, thus seems to be represented in the motor cortex so that it can be triggered by the mere presence of an acting hand in the peripersonal space.Peer reviewe

All that glitters is not BOLD: inconsistencies in functional MRI

The blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) signal is a widely-accepted marker of brain activity. The acquisition parameters (APs) of fMRI aim at maximizing the signals related to neuronal activity while minimizing unrelated signal fluctuations. Currently, a diverse set of APs is used to acquire BOLD fMRI data. Here we demonstrate that some fMRI responses are alarmingly inconsistent across APs, ranging from positive to negative, or disappearing entirely, under identical stimulus conditions. These discrepancies, resulting from non-BOLD effects masquerading as BOLD signals, have remained largely unnoticed because studies rarely employ more than one set of APs. We identified and characterized non-BOLD responses in several brain areas, including posterior cingulate cortex and precuneus, as well as AP-dependence of both the signal time courses and of seed-based functional networks, noticing that AP manipulation can inform about the origin of the measured signals.Peer reviewe

Gaze-Direction-Based MEG Averaging During Audiovisual Speech Perception

To take a step towards real-life-like experimental setups, we simultaneously recorded magnetoencephalographic (MEG) signals and subject's gaze direction during audiovisual speech perception. The stimuli were utterances of /apa/ dubbed onto two side-by-side female faces articulating /apa/ (congruent) and /aka/ (incongruent) in synchrony, repeated once every 3 s. Subjects (N = 10) were free to decide which face they viewed, and responses were averaged to two categories according to the gaze direction. The right-hemisphere 100-ms response to the onset of the second vowel (N100m’) was a fifth smaller to incongruent than congruent stimuli. The results demonstrate the feasibility of realistic viewing conditions with gaze-based averaging of MEG signals

Kohti konvergenssitutkimusta

Solving complex 'wicked' problems requires multidisciplinary approaches. Here I introduce convergence research, a concept still relatively unknown in Finland. Convergence research involves collaboration across various disciplines to achieve common goals by integrating knowledge, skills, and approaches. Convergence research requires attitude changes from researchers, universities, and funders, as well as efforts for creating a shared language, recognizing individual researchers' contributions, and reforming university recruitment and evaluation practices. The pillars of convergence research include a shared research problem, effective communication, researcher-driven formation of teams, respect for other fields, and appropriate interpersonal chemistry.Solving complex 'wicked' problems requires multidisciplinary approaches. Here I introduce convergence research, a concept still relatively unknown in Finland. Convergence research involves collaboration across various disciplines to achieve common goals by integrating knowledge, skills, and approaches. Convergence research requires attitude changes from researchers, universities, and funders, as well as efforts for creating a shared language, recognizing individual researchers' contributions, and reforming university recruitment and evaluation practices. The pillars of convergence research include a shared research problem, effective communication, researcher-driven formation of teams, respect for other fields, and appropriate interpersonal chemistry

Enhanced Extrastriate Activation during Observation of Distorted Finger Postures

Hand and finger postures of other people are important body language cues that strongly contribute to the observer's decision about the person's intentions, thoughts, and attentional state. We compared neuromagnetic cortical activation elicited by color images of natural and distorted finger postures. The distorted postures contained computer-deformed joint angles and thereby easily caught the observer's attention. From about 260 msec onwards, extrastriate occipital areas of both hemispheres were activated more strongly by distorted than natural finger postures. We interpret this result as an early topdown effect of emotional valence on the processing of unusual hand shapes in the extrastriate visual cortex.Peer reviewe

The Human Auditory Sensory Memory Trace Persists about 10 sec: Neuromagnetic Evidence

Neuromagnetic responses were recorded to frequent "standard tones of l000 Hz and to infrequent 1100-Hz "deviant" tones with a 24-channel planar SQUID gradiometer. Stimuli were presented at constant interstimulus intervals (ISIs) ranging from 0.75 to 12 sec. The standards evoked a prominent 100-msec response, N100m, which increased in amplitude with increasing ISI. N100m could be dissociated into two subcomponents with different source areas. The posterior component, N100m2, increased when the ISI grew up to 6 sec, whereas the more anterior component, N100m2, probably continued its growth beyond the 12-sec ISI. At ISIs from 0.75 to 9 sec, the deviants elicited additionally a mismatch field (MMF). The equivalent sources of both N100m and MMF were at the supra-temporal auditory cortex. We assume that auditory stimuli leave in the auditory system a trace that affects the processing of the subsequent stimuli. The decrement of the N100m amplitude as well as elicitation of MMF can be considered as indirect evidence of active traces. A behavioral estimate of the persistence of the sensory auditory memory was obtained in a separate experiment in which the subject compared, without attending to the stimuli, tones presented at the daerent ISIs. The subjects discriminated the stimuli better than merely by chance at ISIs of 0.75-9 sec. The ISI dependence of the behavioral estimate as well as of N100m2 and MMF are similar enough to suggest a common underlying mechanism that retains information for a period of about 10 sec.Peer reviewe

Stimulus-Rate Sensitivity Discerns Area 3b of the Human Primary Somatosensory Cortex

Previous studies have shown that the hemodynamic response of the primary somatosensory cortex (SI) to electrical median nerve stimulation doubles in strength when the stimulus rate (SR) increases from 1 to 5 Hz. Here we investigated whether such sensitivity to SR is homogenous within the functionally different subareas of the SI cortex, and whether SR sensitivity would help discern area 3b among the other SI subareas. We acquired 3-tesla functional magnetic resonance imaging (fMRI) data from nine healthy adults who received pneumotactile stimuli in 25-s blocks to three right-hand fingers, either at 1, 4, or 10 Hz. The main contrast (all stimulations pooled vs. baseline), applied to the whole brain, first limited the search to the whole SI cortex. The conjunction of SR-sensitive contrasts [4 Hz − 1 Hz] > 0 and [10 Hz − 1 Hz] > 0 ([4Hz − 1Hz] + [10Hz − 1Hz] > 0), applied to the SI cluster, then revealed an anterior-ventral subcluster that reacted more strongly to both 10-Hz and 4-Hz stimuli than to the 1-Hz stimuli. No other SR-sensitive clusters were found at the group-level in the whole-brain analysis. The site of the SR-sensitive SI subcluster corresponds to the canonical position of area 3b; such differentiation was also possible at the individual level in 5 out of 9 subjects. Thus the SR sensitivity of the BOLD response appears to discern area 3b among other subareas of the human SI cortex.Peer reviewe

Feature-Specific Information Processing Precedes Concerted Activation in Human Visual Cortex

Current knowledge about the precise timing of visual input to the cortex relies largely on spike timings in monkeys and evoked-response latencies in humans. However, quantifying the activation onset does not unambiguously describe the timing of stimulus-feature-specific information processing. Here, we investigated the information content of the early human visual cortical activity by decoding low-level visual features from single-trial magnetoencephalographic (MEG) responses. MEG was measured from nine healthy subjects as they viewed annular sinusoidal gratings (spanning the visual field from 2 to 10° for a duration of 1 s), characterized by spatial frequency (0.33 cycles/degree or 1.33 cycles/degree) and orientation (45° or 135°); gratings were either static or rotated clockwise or anticlockwise from 0 to 180°. Time-resolved classifiers using a 20 ms moving window exceeded chance level at 51 ms (the later edge of the window) for spatial frequency, 65 ms for orientation, and 98 ms for rotation direction. Decoding accuracies of spatial frequency and orientation peaked at 70 and 90 ms, respectively, coinciding with the peaks of the onset evoked responses. Within-subject time-insensitive pattern classifiers decoded spatial frequency and orientation simultaneously (mean accuracy 64%, chance 25%) and rotation direction (mean 82%, chance 50%). Classifiers trained on data from other subjects decoded the spatial frequency (73%), but not the orientation, nor the rotation direction. Our results indicate that unaveraged brain responses contain decodable information about low-level visual features already at the time of the earliest cortical evoked responses, and that representations of spatial frequency are highly robust across individuals.Peer reviewe