Peter Sörös

Neuroimaging evidence for cortical involvement in the preparation and in the act of swallowing

This study employed whole head magnetoencephalography and synthetic aperture magnetometry to investigate the cortical topography of the preparation and the execution of volitional and reflexive water swallowing and of a simple tongue movement. Concerning movement execution, activation of the mid-lateral primary sensorimotor cortex was strongly lateralized to the left during volitional water swallowing, less strongly lateralized to the left during reflexive water swallowing, and not lateralized at all during tongue movement. In contrast, the preparation for both volitional water swallowing and tongue movement showed a bilateral activation of the primary sensorimotor cortex. No activation was seen prior to reflexive water swallowing. Activation of the left insula and frontal operculum was observed only during both the preparation and the execution of volitional water swallowing. These new findings suggest a left hemispheric dominance for the cortical control of swallowing in humans.

Functional reorganization of the human primary somatosensory cortex after acute pain demonstrated by magnetoencephalography

The somatosensory system is capable of functional reorganization following peripheral denervation or training. Studies on human amputees with phantom limb pain provided evidence that these reorganizational changes are modulated through nociceptive input. In the present study we used magnetoencephalographic recordings of six healthy volunteers to assess whether acute pain by itself causes a reorganization of the primary somatosensory cortex. After the induction of an intense experimental pain at the thenar of the left hand by intradermal injection of capsaicin, the extent of the cortical hand representation and the distance between the hand representation and the localization of the lip decreased. A likely mechanism for this acute reorganization is that pain induced hyperresponsiveness of the left thenar to tactile input from neighboring body sites.

Cortical asymmetries of the human somatosensory hand representation in right- and left-handers

Hemispheric asymmetry is known for higher brain functions like language and attention. We tested whether such an asymmetry also exists in the representation of elementary sensory functions. Magnetic source imaging was used to compare the cortical somatosensory hand representation in seven right- and five left-handed individuals. In all right-handers the representation of the dominant hand was larger than the contralateral one in the corresponding hemispheres. In contrast, only two out of five left-handers revealed a larger representation of the dominant left hand compared to the right one. In agreement with previous findings on the lateralization of language and attention, there is a strong correlation between handedness and the extent of the cortical hand representation in right-, but not in left-handers. We conclude that a profound functional hemispheric asymmetry also exists in primary sensory cortices.

Phantom sensations following acute pain.

Abstract In human amputees with painful phantom sensations, mislocalizations of tactile stimuli to the phantom increase with the amount of cortical representational reorganization and the extent of phantom pain. A similar phenomenon was incidentally encountered in healthy subjects. For reasons unrelated to the question of mislocalization, we performed a study involving the application of experimental acute pain to the hand followed by non‐noxious tactile stimulation of the ipsilateral lip. During lip stimulation, two out of six subjects spontaneously reported perceiving an additional phantom‐like sensation in the hand synchronously to the non‐noxious lip stimulation. Similar, although more diffuse, phantom sensations were observed in two out of seven additional subjects who were then tested specifically for this effect. The observation is compatible with a pain‐induced hyperresponsiveness of the cortical hand area to somatotopically adjacent inputs from the lip. This suggests that, even in the absence of deafferentation, pain can lead to a representational reorganization.

Current source density distribution of sleep spindles in humans as found by synthetic aperture magnetometry.

Previous magnetoencephalography (MEG) studies of sleep spindles have identified a complex and widespread distribution in parietal and frontal cortices by fitting a dipolar model to the data. In this study, we used a whole-head 151-channel MEG system with simultaneous electroencephalography (EEG) recording in eight normal subjects. All subjects fell asleep during stage 2 and 3; EEG spindles have been observed in all cases. The current source density distribution of sleep spindles in the 10-15 Hz frequency band was localized by means of synthetic aperture magnetometry, and statistically tested using a permutation analysis. Source locations of the sleep spindles were found primarily in the frontal cortex, including dorsolateral and medial prefrontal areas, as well as the parietal cortex, including the vicinity of the primary sensorimotor areas. These results suggest that sleep spindles are similar in frequency content and spatial location to mu rhythm, and that these two oscillatory activities might also have a common neural basis and physiological meaning.

Cluster headache after dental extraction: implications for the pathogenesis of cluster headache?

Cluster headache (CH) is a disorder of unilateral attacks of severe periorbital, supraorbital or temporal pain, lasting 15±180 min (1). In general, attacks are accompanied by autonomic symptoms, i.e. ipsilateral miosis, lacrimation, conjunctival injection, nasal congestion and rhinorrhea. The episodic form of CH, found in about 80% of all CH patients, is characterized by its distinct temporal pattern. One to 8 headache attacks per day occur during bouts lasting 2 weeks to 3 months, followed by remission for months or years. Along with migraine and other rare hemicranias, CH is regarded as a primary headache disorder. More than 250 years after the ®rst known description of CH by van Swieten (2), the pathophysiology of this disorder is still controversial. Recent brain imaging studies demonstrated the activation of the ipsilateral hypothalamus during a CH attack (3). Moreover, morphological enlargement of the hypothalamus found in CH sufferers suggests an inborn predisposition for the development of CH (4). In this report, we present two patients who developed ipsilateral CH shortly after the extraction of an ipsilateral molar tooth. We review the literature on CH associated with head trauma or structural brain lesions and discuss the implications of these cases for the pathogenesis of CH.

Auditory temporal processing in healthy aging: a magnetoencephalographic study

BackgroundImpaired speech perception is one of the major sequelae of aging. In addition to peripheral hearing loss, central deficits of auditory processing are supposed to contribute to the deterioration of speech perception in older individuals. To test the hypothesis that auditory temporal processing is compromised in aging, auditory evoked magnetic fields were recorded during stimulation with sequences of 4 rapidly recurring speech sounds in 28 healthy individuals aged 20 – 78 years.ResultsThe decrement of the N1m amplitude during rapid auditory stimulation was not significantly different between older and younger adults. The amplitudes of the middle-latency P1m wave and of the long-latency N1m, however, were significantly larger in older than in younger participants.ConclusionThe results of the present study do not provide evidence for the hypothesis that auditory temporal processing, as measured by the decrement (short-term habituation) of the major auditory evoked component, the N1m wave, is impaired in aging. The differences between these magnetoencephalographic findings and previously published behavioral data might be explained by differences in the experimental setting between the present study and previous behavioral studies, in terms of speech rate, attention, and masking noise. Significantly larger amplitudes of the P1m and N1m waves suggest that the cortical processing of individual sounds differs between younger and older individuals. This result adds to the growing evidence that brain functions, such as sensory processing, motor control and cognitive processing, can change during healthy aging, presumably due to experience-dependent neuroplastic mechanisms.

Time course of focal slow wave activity in transient ischemic attacks and transient global amnesia as measured by magnetoencephalography

In this longitudinal study multichannel MEG was used to localize and to quantify focal pathological spontaneous neuromagnetic activity in six patients with transient ischemic attacks (TIA) and two patients with transient global amnesia (TGA). Slow (2–6 Hz) and beta (14–30 Hz) activity were monitored up to 10 weeks. Results were compared with normative data, and changes over time were statistically analyzed. MEG detected pathological activity that persisted clinical symptoms. Focal slow activity originating from sensorimotor (TIA) and mesiotemporal (TGA) cortices exceeded normal values up to 14 times during the first hours after the attack and recovered to normal within 11 days. Focal beta activity was not useful to monitor the time course of TIA or TGA.

Enucleation and development of cluster headache: a retrospective study

BackgroundCluster headache (CH) is a neurovascular, primary headache disorder. There are, however, several case reports about patients whose CH started shortly after a structural brain disease or trauma. Motivated by a patient who developed CH 3 weeks after the removal of an eye and by similar case reports, we tested the hypothesis that the removal of an eye is a risk factor for CH.MethodsA detailed headache questionnaire was filled out by 112 patients on average 8 years after enucleation or evisceration of an eye.ResultsWhile 21 % of these patients experienced previously unknown headaches after the removal of an eye, no patient fulfilled the diagnostic criteria for CH.ConclusionOur data does not suggest that the removal of an eye is a major risk factor for the development of CH.

Peripheral Autonomic Potentials in Primary Headache and Drug-Induced Headache

Autonomic functions of different primary headache types have been investigated in several studies, most of them analyzing cardiovascular reflex mechanisms or biochemical changes. The results are contradictory; only in tension-type headache and in cluster headache has a sympathetic hypofunction been shown in a preponderance of studies. We analyzed the peripheral autonomous potentials (PAPs) in different primary headache types and in drug-induced headache and compared the results with those of healthy subjects and of patients with low back pain. Latencies of PAPs were significantly increased in all headache types but not in low back pain; amplitudes of PAPs did not show significant differences compared to healthy subjects. Patients with a long duration of drug abuse had increased PAP latencies, whereas patients with a high number of migraine attacks per year had decreased latencies. Our data suggest that sympathetic hypo-function as measured by PAP latencies is a general phenomenon in headache but not in all pain syndromes. Drug abuse leads to an increase of this hypofunction. While measuring PAPs is not an appropriate method by which to differentiate between headache disorders, it allows assessment of autonomic disturbances in primary and drug-induced headache.