PubMed Health⌕ Search

Biomedical subjects

Nina Forss

Publications and source records attributed to Nina Forss.

12 recordsLinked to original sources
PubMed2006

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.

Adult↗
PubMed2006

Magnetoencephalography in neurosurgery.

OBJECTIVE: To present applications of magnetoencephalography (MEG) in studies of neurosurgical patients. METHODS: MEG maps magnetic fields generated by electric currents in the brain, and allows the localization of brain areas producing evoked sensory responses and spontaneous electromagnetic activity. The identified sources can be integrated with other imaging modalities, e.g., with magnetic resonance imaging scans of individual patients with brain tumors or intractable epilepsy, or with other types of brain imaging data. RESULTS: MEG measurements using modern whole-scalp instruments assist in tailoring individual therapies for neurosurgical patients by producing maps of functionally irretrievable cortical areas and by identifying cortical sources of interictal and ictal epileptiform activity. The excellent time resolution of MEG enables tracking of complex spaciotemporal source patterns, helping, for example, with the separation of the epileptic pacemaker from propagated activity. The combination of noninvasive mapping of subcortical pathways by magnetic resonance imaging diffusion tensor imaging with MEG source localization will, in the near future, provide even more accurate navigational tools for preoperative planning. Other possible future applications of MEG include the noninvasive estimation of language lateralization and the follow-up of brain plasticity elicited by central or peripheral neural lesions or during the treatment of chronic pain. CONCLUSION: MEG is a mature technique suitable for producing preoperative "road maps" of eloquent cortical areas and for localizing epileptiform activity.

Brain Diseases↗
PubMed2005

Mirror-like spread of chronic pain.

The spread of chronic pain from its initial site of presentation is common, but the mechanisms of the spread are unknown. Here the authors present neurophysiologic evidence of altered interhemispheric conduction in a patient with a mirror-like spread of complex regional pain syndrome symptoms.

Adult↗
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

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↗
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

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↗
PubMed2002

Cortical sensorimotor alterations in Unverricht-Lundborg disease patients without generalized seizures.

We investigated cortical functions of two Unverricht-Lundborg disease (ULD) patients suffering from myoclonic jerks, but no generalized tonic-clonic seizures. Somatosensory cortical responses were recorded to median nerve stimuli and coherence was calculated between cortical and muscle signals during isometric contraction of hand muscle. In contrast to ULD patients with generalized tonic-clonic seizures, responses of the primary somatosensory (SI) cortex were only slightly enhanced in the left and normal in the right hemisphere, and no early responses were observed in the ipsilateral SI. Cortex-muscle coherence was remarkably enhanced. We conclude that in ULD patients without generalized tonic-clonic seizures, both the excitability of the SI and transcallosal conduction are relatively normal, probably decreasing susceptibility to generalized seizures. Disturbed cortical control of muscle contraction indicates selective alteration of the motor cortex activation.

Adolescent↗
PubMed2002

Left-hemisphere-dominant SII activation after bilateral median nerve stimulation.

We used bilateral median nerve stimuli to find out possible hemispheric dominance in the activation of the second somatosensory cortex, SII. Somatosensory evoked fields (SEFs) were recorded from 14 healthy adults (7 right-handed, 7 left-handed) with a 306-channel neuromagnetometer. Electrical stimuli were applied once every 3 s simultaneously either to the left and right median nerves at the wrists or to the palmar skin of both thumbs. Sources of SEFs were modeled with four current dipoles, located in the SI and SII cortices of both hemispheres. The SI activation strengths did not differ between the hemispheres, whereas the SII responses were significantly stronger in the left than in the right hemisphere. In right-handers, the left/right SII ratios were 1.9 and 1.8 for wrist and thumb stimuli, respectively. The corresponding values were 1.5 and 1.7 in left-handers. The results indicate handedness-independent functional specialization of the human SII cortices.

Adult↗
PubMed2002

Modulated activation of the human SI and SII cortices during observation of hand actions.

Neurons in area F5 of the monkey premotor cortex are activated during both execution and observation of hand actions. A similar "mirror-neuron system" seems to exist also in the human brain, including at least the superior temporal sulcus region, Broca's area, and the primary motor cortex. We recorded somatosensory evoked fields in response to median nerve stimulation from nine healthy subjects during (i) rest, (ii) manipulation of a small object, and (iii) observation of the same action to find out to what extent the somatosensory cortices display behavior similar to the human mirror-neuron system. SI signals were enhanced and SII signals suppressed during both manipulation and observation, except when the right manipulating hand was stimulated. Our results suggest that the SI and SII cortices contribute to the human mirror-neuron system, possibly providing information necessary for preserving the sense of self during action observation.

Adult↗
PubMed2002

Altered central sensorimotor processing in patients with complex regional pain syndrome.

Alterations in tactile sensitivity are common in patients with chronic pain. Recent brain imaging studies have indicated that brain areas activated by acute experimental pain partly overlap with areas processing innocuous tactile stimuli. However, the possible effect of chronic pain on central tactile processing has remained unclear. We have examined, both clinically and with whole-head magnetoencephalography, six patients suffering from complex regional pain syndrome (CRPS) of the upper limb. The cortical somatosensory responses were elicited by tactile stimuli applied to the fingertips and the reactivity of spontaneous brain oscillations was monitored as well. Tactile stimulation of the index finger elicited an initial activation at 65 ms in the contralateral SI cortex, followed by activation of the ipsi- and contralateral SII cortices at about 130 ms. The SI responses were 25-55% stronger to stimulation of the painful than the healthy side. The distance between SI representations of thumb and little finger was significantly shorter in the hemisphere contralateral than ipsilateral to the painful upper limb. In addition, reactivity of the 20-Hz motor cortex rhythm to tactile stimuli was altered in the CRPS patients, suggesting modified inhibition of the motor cortex. These results imply that chronic pain may alter central tactile and motor processing.

Adult↗