Biomedical subjects

Riitta Hari

Publications and source records attributed to Riitta Hari.

At least 19 recordsLinked to original sources

PubMed2005

Oscillatory motor cortex-muscle coupling during painful laser and nonpainful tactile stimulation.

Noxious stimulation activates-in addition to the brain structures related to sensory, emotional, and cognitive components of pain-also the brain's motor system. Effect of noxious input on the primary motor (MI) cortex remains, however, poorly understood. To characterize this effect in more detail, we quantified the ongoing oscillatory communication between the MI cortex and hand muscles during selectively noxious laser stimulation. The subjects maintained an isometric contraction of finger muscles while receiving the laser stimuli to the dorsum of the hand. Tactile stimuli with well-known effects on the MI cortex reactivity served as control stimuli. Cortex-muscle coherence was computed between magnetoencephalographic (MEG) signals from the contralateral MI and electromyographic (EMG) signals from the hand muscles. Statistically significant coherence at approximately 20 Hz was found in 6 out of 7 subjects. The coherence increased phasically after both types of stimuli but significantly later after laser than tactile stimuli (mean +/- SEM peak latencies 1.05 +/- 0.12 s vs. 0.58 +/- 0.06 s; P < 0.05), and the coherence increase lasted longer after laser than tactile stimuli (0.87 +/- 0.09 s vs. 0.50 +/- 0.06 s, P < 0.05). The observed coherence increase could be related to stabilization of the motor-cortex control after sensory input. Our findings add to the clinically interesting evidence about the cortical pain-motor system interaction.

Adult↗

PubMed2005

Reproducibility of cortex-muscle coherence.

Cortex-muscle coherence is a frequency-analysis technique that has been increasingly applied in the investigation of movement disorders. To study the intra- and inter-session stability of the cortex-muscle coherence, we recorded from 12 healthy subjects magnetoencephalographic (MEG) and surface electromyographic (EMG) signals during unilateral isometric contractions of the left- and right-hand muscles. Two identical measurements were performed during one session, and the session was repeated once after about 1 year. In one experienced subject, the recordings were repeated seven times within 20 months. The MEG-EMG coherence exceeded the noise level in 10 out of 12 subjects. Both the frequency (correlation coefficient r = 0.77-0.93, P < 0.01) and strength (r = 0.78-0.91, P < 0.01) of coherence were well reproducible within each session for both left- and right-sided contractions. The inter-session reproducibility was high for the mean of cumulative coherence frequency (r = 0.90-0.95, P < 0.01), but relatively low for coherence strength (r = 0.43-0.59, P > 0.05). The results for one subject participating in 8 repeated sessions strongly supported the results of the whole group. Thus, intra-session reproducibility of both strength and frequency of the cortex-muscle coherence is good and studies comparing different conditions at the group level within one session are feasible. However, caution is needed when interpreting absolute levels or changes in the strength of coherence in single subjects between the sessions.

Adult↗

PubMed2005

Yearning to yawn: the neural basis of contagious yawning.

Yawning is contagious: Watching another person yawn may trigger us to do the same. Here we studied brain activation with functional magnetic resonance imaging (fMRI) while subjects watched videotaped yawns. Significant increases in the blood oxygen level dependent (BOLD) signal, specific to yawn viewing as contrasted to viewing non-nameable mouth movements, were observed in the right posterior superior temporal sulcus (STS) and bilaterally in the anterior STS, in agreement with the high affinity of STS to social cues. However, no additional yawn-specific activation was observed in Broca's area, the core region of the human mirror-neuron system (MNS) that matches action observation and execution. Thus, activation associated with viewing another person yawn seems to circumvent the essential parts of the MNS, in line with the nature of contagious yawns as automatically released behavioural acts-rather than truly imitated motor patterns that would require detailed action understanding. The subjects' self-reported tendency to yawn covaried negatively with activation of the left periamygdalar region, suggesting a connection between yawn contagiousness and amygdalar activation.

Adolescent↗

PubMed2005

Brain correlates of subjective reality of physically and psychologically induced pain.

Meaningful behavior requires successful differentiation of events surfacing from one's mind from those arising from the external world. Such judgements may be especially demanding during pain because of the strong contribution from psychological factors to this experience. It is unknown how the subjective reality of pain (SRP) is constructed in the human brain, and neuronal mechanisms of the subjective reality are poorly understood in general. To address these questions, 14 suggestion-prone healthy subjects rated reality of pain that was induced either by laser pulses to the skin or by hypnotic suggestion during functional MRI. Both pain states were associated with activation of the brain's pain circuitry. During laser stimulation, the sensory parts of this circuitry were activated more strongly, and their activation strengths correlated positively with the SRP. During suggestion-induced pain, the reality estimates were lower and correlated positively with activation strengths in the rostral and perigenual anterior cingulate cortex and in the pericingulate regions of the medial prefrontal cortex; a similar trend was evident during laser-induced pain. These findings support the view that information about sensory-discriminative characteristics of pain contributes to the SRP. Differences in such information between physically and psychologically induced pain, however, could be quantitative rather than qualitative and therefore insufficient for judging the reality of pain without knowledge about the source of this information. The medial prefrontal cortex is a likely area to contribute to such source monitoring.

Adult↗

PubMed2005

Common cortical network for first and second pain.

We measured, with whole-scalp magnetoencephalography, evoked fields from 10 healthy subjects to 1-ms thulium-laser stimuli that selectively activated nociceptive nerve fibers. The stimuli were delivered to the dorsum of the subject's left hand. The earliest cortical responses peaked at 165 +/- 7 ms, agreeing with the conduction velocity of Adelta-fibers. To stimulate unmyelinated C-fibers, we modified the method of Bragard et al. [Bragard, D., Chen, A.C., Plaghki, L., 1996. Direct isolation of ultra-late (C-fibre) evoked brain potentials by CO2 laser stimulation of tiny cutaneous surface areas in man. Neurosci. Lett. 209, 81-84], by decreasing the total energy of the laser beam and by restricting the size of the stimulated skin area to 0.2-0.3 mm2. The earliest cortical responses to these stimuli peaked at 811 +/- 14 ms. Bilateral activation of the SII cortices was detected in all 10 subjects to Adelta and in 8 subjects to C stimuli, emphasizing the importance of the SII cortex in processing of pain. Additional activation was observed in the posterior parietal cortex (PPC), probably related to sensorimotor coordination targeted to produce precise motor acts that reduce or prevent the pain; the PPC activation may have been accentuated by the required continuous evaluation of the perceived pain. In contrast to some earlier studies, we did not observe activation of the primary somatosensory cortex (SI). Additional activations to both types of stimuli were detected in the cingulate cortex (three subjects) and in the bilateral insular cortex (two subjects). These results implicate that the nociceptive inputs mediated by the Adelta- and C-fibers are processed in a common cortical network in different time windows. Reliable temporospatial characterization of cortical responses to first and second pain offers a unique tool for basic and clinical neuroscience to study the two distinctive pain fiber systems at cortical level.

Adult↗

PubMed2005

Diffusion tensor imaging and tractography of distal peripheral nerves at 3 T.

OBJECTIVE: We studied whether distal peripheral nerves could be imaged using quantitative diffusion tensor imaging (DTI) with a 3-T MRI scanner, and visualized using tractography. METHODS: Altogether 6 healthy subjects were studied. The diffusion was quantified with apparent diffusion coefficient (ADC) and fractional anisotropy (FA) maps, and the direction of main diffusivity was visualized with color-coded orientation maps and tractography. RESULTS: We present the first DTI and tractography results of human distal peripheral nerves. The courses of median, ulnar, and radial nerves in the upper limb and of tibial and peroneal nerves in the lower limb were first analyzed quantifying ADC and FA, and then visualized in 3D with tractography. Tractography illustrated nicely the 3D courses of both upper and lower limb nerves which were reliably distinguished from the surrounding muscle tissue and ligaments. CONCLUSIONS: Quantitative DTI and tractography can be used to image and visualize distal peripheral nerves. SIGNIFICANCE: DTI is a quantitative method that could provide useful information for the diagnosis and follow-up of nerve lesions, entrapments, and regeneration. Peripheral nerves as well-delineated structures also containing abundant branching into bundles of different diameters, could be used as 'living phantoms' for testing and validating different tractography methods.

Adult↗

PubMed2005

Broca's region: from action to language.

Broca's region, classically considered a motor speech-production area, is involved in action understanding and imitation. It also seems to help in sequencing of actions. Broca's region might have evolved for interindividual communication, both by gestures and speech.

Animals↗

PubMed2004

Viewing speech modulates activity in the left SI mouth cortex.

The ability to internally simulate other persons' actions is important for social interaction. In monkeys, neurons in the premotor cortex are activated both when the monkey performs mouth or hand actions and when it views or listens to actions made by others. Neuronal circuits with similar "mirror-neuron" properties probably exist in the human Broca's area and primary motor cortex. Viewing other person's hand actions also modulates activity in the primary somatosensory cortex SI, suggesting that the SI cortex is related to the human mirror-neuron system. To study the selectivity of the SI activation during action viewing, we stimulated the lower lip (with tactile pulses) and the median nerves (with electric pulses) in eight subjects to activate their SI mouth and hand cortices while the subjects either rested, listened to other person's speech, viewed her articulatory gestures, or executed mouth movements. The 55-ms SI responses to lip stimuli were enhanced by 16% (P<0.01) in the left hemisphere during speech viewing whereas listening to speech did not modulate these responses. The 35-ms responses to median-nerve stimulation remained stable during speech viewing and listening. Own mouth movements suppressed responses to lip stimuli bilaterally by 74% (P<0.001), without any effect on responses to median-nerve stimuli. Our findings show that viewing another person's articulatory gestures activates the left SI cortex in a somatotopic manner. The results provide further evidence for the view that SI is involved in "mirroring" of other persons' actions.

Adult↗

PubMed2004

Abnormal response recovery in the right somatosensory cortex of dyslexic adults.

Somatosensory evoked fields (SEFs) to repetitive tactile stimuli were recorded from eight dyslexic and eight normal-reading adults. Three successive stimuli, produced by diaphragms driven by compressed air, were delivered to thumb, index finger and thumb in sequence, with stimulus-onset asynchronies (SOAs) of 100 and 200 ms in different runs. Both hands were stimulated alternatingly with an intertrain interval of 1 s, and the responses were recorded with a whole-scalp neuromagnetometer. Whereas the primary somatosensory cortex responses to the first stimuli of the trains did not differ between dyslexics and controls, responses to the second stimuli (and the ratios of second to first responses) were significantly smaller in dyslexic than in control subjects in the right hemisphere (differences 41 and 28% for response amplitudes at the 100 and 200 ms SOAs). The results agree with the proposed pansensory nature of temporal processing deficits in dyslexia, specifically demonstrating abnormal response recovery in the right somatosensory cortex.

Adaptation, Physiological↗

PubMed2004

Face recognition and cortical responses show similar sensitivity to noise spatial frequency.

To find cortical correlates of face recognition, we manipulated the recognizability of face images in a parametric manner by masking them with narrow-band spatial noise. Face recognition performance was best at the lowest and highest noise spatial frequencies (NSFs, 2 and 45 c/image, respectively), and degraded gradually towards central NSFs (11-16 c/image). The strength of the 130-180 ms neuromagnetic response (M170) in the temporo-occipital cortex paralleled the recognition performance, whereas the mid-occipital response at 70-120 ms acted in the opposite manner, being strongest for the central NSFs. To noise stimuli without faces, M170 was small and rather insensitive to NSF, whereas the mid-occipital responses resembled closely the responses to the combined face and noise stimuli. These results suggest that the 100 ms mid-occipital response is sensitive to the central spatial frequencies that are critical for face recognition, whereas the M170 response is sensitive to the visibility of a face and closely related to face recognition.

Adult↗

PubMed2004

Suppressed responses to self-triggered sounds in the human auditory cortex.

Humans are assumed to predict the sensory consequences of their own actions by means of forward models that enable discrimination between self-produced and external sensory signals. Here we tested whether responses in the human auditory cortex would differ to self-triggered versus externally triggered tones. The responses were recorded with a whole-scalp neuromagnetometer from 12 healthy subjects who either themselves triggered a tone by pressing a button once every 5 s or passively listened to externally triggered tones, presented in an identical sound sequence. Sources of the auditory N100m responses, peaking approximately 90 ms after sound onset in the supratemporal auditory cortex, were significantly weaker to self-triggered than to externally triggered sounds (suppressions 24 +/- 7% and 18 +/- 4% in the left and right hemispheres, respectively). These results support the existence of a forward model that predicts the auditory consequences of the subject's own motor acts on the environment--even with a tool--and thereby enables discrimination between self-produced and external sounds.

Acoustic Stimulation↗

PubMed2004

Abnormal imitation-related cortical activation sequences in Asperger's syndrome.

Subjects with Asperger's syndrome (AS) are impaired in social interaction and imitation, but the underlying brain mechanisms are poorly understood. Because the mirror-neuron system (MNS) that matches observed and executed actions has been suggested to play an important role in imitation and in reading of other people's intentions, we assessed MNS functions in 8 adult AS subjects and in 10 healthy control subjects during imitation of still pictures of lip forms. In the control subjects, cortical activation progressed in 30 to 80-millisecond steps from the occipital cortex to the superior temporal sulcus, to the inferior parietal lobe, and to the inferior frontal lobe, and finally, 75 to 90 milliseconds later, to the primary motor cortex of both hemispheres. Similar activation sites were found in AS subjects but with slightly larger scatter. Activation of the inferior frontal lobe was delayed by 45 to 60 milliseconds and activations in the inferior frontal lobe and in the primary motor cortex were weaker than in control subjects. The observed abnormal premotor and motor processing could account for a part of imitation and social impairments in subjects with AS.

Adult↗

PubMed2004

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.

Adult↗

PubMed2004

Cortical activation during a spatiotemporal tactile comparison task.

Tactile sensory memory is needed to infer shape or motion from the spatiotemporal pattern of sensory input during manual exploration. Here we applied triplets of pressure pulses to the fingertips of subjects who were asked to respond when successive triplets were the same (COMPARE task) or when a particular stimulus was included in a triplet (CONTROL task). Stimulus sequences (30 s) alternated with rest blocks (30 s) and functional magnetic resonance images (fMRIs) were acquired in a 1.5-T scanner. During the COMPARE task, we found enhanced activation in inferior parietal cortex, supplementary motor area (SMA), and right dorsolateral prefrontal cortex (DLPFC). Activation of DLPFC is likely to be related to the attempt to memorize the stimulus sequences and activations of SMA and inferior parietal cortex to the analysis of temporospatial tactile patterns and, more generally, to guidance of haptic exploration. In addition, task-specific activation was seen in anterior cingulate gyrus, possibly related to the high mental effort required by the comparison task. Our rhythmic tactile stimulus as such, without any task-specific enhancement, activated also left cerebellum and (mainly left) putamen, supporting the idea that these structures are related to perception of temporal order of tactile stimuli.

Adult↗

PubMed2004

Activation of the human primary motor cortex during observation of tool use.

Tool use is a characteristic human trait, requiring motor skills that are largely learned by imitation. A neural system that supports imitation and action understanding by directly matching observed actions and their motor counterparts has been found in the human premotor and motor cortices. To test whether this "mirror-neuron system" (MNS) would be activated by observation of tool use, we recorded neuromagnetic oscillatory activity from the primary motor cortex of 10 healthy subjects while they observed the experimenter to use chopsticks in a goal-directed and non-goal-directed manner. The left and right median nerves were stimulated alternatingly, and the poststimulus rebounds of the approximately 20-Hz motor-cortex rhythms were quantified. Compared with the rest condition, the level of the approximately 20-Hz rhythm was suppressed during observation of both types of tool use, indicating activation of the primary motor cortex. The suppression was on average 15-17% stronger during observation of goal-directed than non-goal-directed tool use, and this difference correlated positively with the frequency of subjects' chopstick use during the last year. These results support the view that the motor-cortex activation is related to the observer's ability to understand and imitate motor acts.

Adult↗

PubMed2004

Modulation of motor-cortex oscillatory activity by painful Adelta- and C-fiber stimuli.

Spontaneous approximately 20-Hz oscillations, arising predominantly from the primary motor cortex (MI), are readily observed by magnetoencephalography (MEG). Prior studies have indicated that the level of the approximately 20-Hz rhythm reflects the functional state of the MI cortex: increased 20-Hz level is associated with increased inhibition and suppression of the rhythm with excitation of MI. Close interaction is suggested between pain and the motor system by the association of chronic pain with motor dysfunction and by the alleviation of pain by motor-cortex stimulation. We therefore explored the effect of noxious input on motor-cortex functions by recording MEG signals from nine healthy subjects during selective laser stimulation of Adelta- and C-fibers of the hand. The approximately 20-Hz level was suppressed in the contralateral MI cortex in all nine subjects after painful Adelta- and C-fiber stimuli (P < 0.001). The suppression started 180 +/- 10 ms (mean +/- SEM) after Adelta-fiber stimuli and 820 +/- 30 ms after C-fiber stimuli, and peaked 160-170 ms later. Similar, but about 50% weaker, suppression of the approximately 20-Hz oscillations occurred in seven out of nine subjects in the ipsilateral MI. These results suggest automatic, lateralized, excitation of the MI cortex by noxious Adelta- and C-fiber input.

Adult↗

PubMed2004

Hands help hearing: facilitatory audiotactile interaction at low sound-intensity levels.

Auditory and vibrotactile stimuli share similar temporal patterns. A psychophysical experiment was performed to test whether this similarity would lead into an intermodal bias in perception of sound intensity. Nine normal-hearing subjects performed a loudness-matching task of faint tones, adjusting the probe tone to sound equally loud as a reference tone. The task was performed both when the subjects were touching and when they were not touching a tube that vibrated simultaneously with the probe tone. The subjects chose on average 12% lower intensities (p < 0.01) for the probe tone when they touched the tube, suggesting facilitatory interaction between auditory and tactile senses in normal-hearing subjects.

Adult↗

PubMed2003

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 top-down effect of emotional valence on the processing of unusual hand shapes in the extrastriate visual cortex.

Adult↗