Eosinophilia associated with clozapine.
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Adult↗
Biomedical subjects
J Tiihonen
Publications and source records attributed to J Tiihonen.
Magnetoencephalographic localization of epileptic cortex--impact on surgical treatment.
A 24-channel, planar, superconducting quantum interference device gradiometer, sampling a fourth of the head surface over brain tissue, was used to determine the site of an epileptic focus in a 36-year-old woman with intractable complex partial epilepsy. The other presurgical findings appeared divergent: a large arachnoid cyst over the right parietal convexity, dissimilar interictal electroencephalographic patterns, and several neuropsychological dysfunctions. The equivalent current sources of magnetoencephalographic spikes were in the right posterior temporal region of the cortex, 4 cm apart from the cyst. Surgical exploration of the area pinpointed by magnetoencephalography revealed a pachygyric patch of cortex displaying focal discharges on the electrocorticogram. After resection, a dramatic reduction of seizures occurred. The good agreement between electrocorticography and magnetoencephalography warrants future investigation of multichannel magnetoencephalography as a potential alternative to invasive presurgical recordings.
Adult↗
Neuromagnetic mismatch fields to single and paired tones.
In 8 subjects we recorded multichannel magnetic responses to pitch changes in single 50 msec tones and in tone pairs (oddball paradigm; interstimulus interval 745 msec). Either "A" (1 kHz) was standard (90%) and "B" (1.2 kHz) deviant (10%), or "AA" was standard and "AB" deviant in pairs with onset asynchrony of 75 msec. Subject did not pay attention to the tones. A mismatch field (MMF) was evident in responses to deviants with an equivalent source in the supratemporal auditory cortex, about 1 cm anterior to that for N100m. The MMF source was 3-fold stronger for tone pairs than for single tones.
Adult↗
Fast decrement with stimulus repetition in ERPs generated by neuronal systems involving somatosensory SI and SII cortices: electric and magnetic evoked response recordings in humans.
The effect of stimulus repetition (short trains of stimuli with 1-s inter-stimulus intervals and 15-s inter-train intervals) on both electric and magnetic evoked responses were studied in four subjects. In addition to the later N140 and P300 deflections in electric potentials, a distinct and immediate amplitude decrement was obtained also for the earlier P50 and P100 deflections. The magnetic evoked responses also demonstrated the amplitude decrement for 50 ms (M50) and 100 ms (M100) latency deflections. The time-course and degree of amplitude decrement of the M100 magnetic response corresponded especially well to those of P100 electric deflections. The results thus show the rate effect on electric and magnetic responses at 50 and 100 ms latencies, and further suggest that the electric and magnetic responses, reflecting the activation of somatosensory SI and SII cortical areas at these latencies, respectively, are generated by related neuronal mechanisms.
Adult↗
Modified activity of the human auditory cortex during auditory hallucinations.
Previous reports have shown abnormalities in brain metabolism and evoked responses of schizophrenic patients with hallucinations. The authors recorded electric and magnetic auditory responses during transitory auditory hallucinations in two patients. Small but replicable response delays occurred during hallucinations. The results suggest that the effect of hallucinations on auditory cortex activity is similar to the effect of real sounds.
Acoustic Stimulation↗
Magnetoencephalographic 10-Hz rhythm from the human auditory cortex.
Spontaneous magnetoencephalographic activity was recorded with a 24-SQUID gradiometer over the lateral aspects of the head in 3 healthy adults. All subjects displayed 8-10 Hz rhythmic activity which was not affected by opening of the eyes but was occasionally dampened by auditory stimuli. The equivalent sources of the rhythm were in the supratemporal auditory cortex, and the activity may therefore represent 'idling' of the auditory cortex. Obviously each sensory projection cortex has its own local spontaneous rhythm.
Acoustic Stimulation↗
EEG abnormalities associated with clozapine treatment.
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Clozapine↗
Localization of epileptic foci using a large-area magnetometer and functional brain anatomy.
We used a large-area, 7-channel, first-order superconducting quantum interference device (SQUID) gradiometer to preoperatively determine the sites of epileptic foci in 2 patients with intractable temporal lobe seizures. The equivalent dipoles for the epileptic spikes were located with respect to external landmarks of the skull and in relation to the generation sites of magnetic auditory evoked responses. It was also possible, for the first time, to determine the location of the equivalent source using simultaneously measured data from seven locations only. The sites of the equivalent dipoles, in the right temporal lobe, agreed with the electrocorticographic and depth electrode recordings made during the operation.
Adult↗
Separate finger representations at the human second somatosensory cortex.
We recorded neuromagnetic responses of the second somatosensory cortex in healthy humans. Cutaneous electrical stimulation of fingers elicited a response around 100 ms, with a field pattern agreeing with activation of the second somatosensory cortex in the upper bank of the Sylvian fissure. In an oddball paradigm, with standards presented to the thumb and deviants (10%) to the middle finger, or vice versa, the second somatosensory cortex responses to deviants were almost three times as high in amplitude as those to standards. A similar amplitude enhancement was obtained when the deviants were presented in the absence of the intervening standards but with the same interstimulus interval. The results indicate that an accurate functional representation of different body areas is maintained at the human second somatosensory cortex.
Adult↗
Selective listening modifies activity of the human auditory cortex.
We have studied the effect of selective listening on the neuromagnetic evoked activity of the human auditory cortex. In the word categorization experiment the stimuli were 5-letter words, each beginning with (k). Half of them were targets, i.e., names of animals or plants, and half other meaningful Finnish words. In the duration discrimination experiment equiprobable tones of 425 ms (targets) or 600 ms duration were presented. In both experiments the interstimulus interval (ISI) was 2.3 s and the stimuli of the two classes were presented randomly. Subjects either ignored the stimuli (reading condition) or counted the number of targets (listening condition). The magnetic field over the head was measured with a 7-channel 1st-order SQUID-gradiometer. The stimuli evoked a transient response followed by a sustained field. The transient response did not differ between the two conditions but the sustained field was significantly larger in the listening than reading condition; the increase began 120-200 ms after stimulus onset and continued for several hundred milliseconds. The equivalent source locations of both transient and sustained responses agreed with activation of the supratemporal auditory cortex. In the dichotic listening experiment 25-ms square-wave stimuli were presented randomly and equiprobably either to the left or to the right ear at an ISI of 0.8-1 s, either alone or in presence of a speech masker. Counting the stimuli of either ear resulted in differences between responses to relevant and irrelevant sounds. The difference began 140-150 ms after stimulus onset and peaked at 200-240 ms. During monaural speech masking, N100m was larger for attended than ignored stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Multichannel detection of magnetic compound action fields of median and ulnar nerves.
We have recorded magnetic compound action fields, evoked by median and ulnar nerve stimulation at the wrist, with a 7-channel 1st-order SQUID gradiometer. Responses at cubita, elbow and brachial plexus were usually monophasic, with polarities and field patterns corresponding to the intracellular current flow in the leading edge of the action potential volley.
Action Potentials↗
Magnetic mu rhythm in man.
We report detection of magnetic mu rhythm in four subjects using a large-area seven-channel first-order superconducting quantum interference device gradiometer. The polarity of this activity was opposite at the upper and lower ends of the rolandic fissure, and during the sharp transients the field patterns could be satisfactorily explained by a current dipole model. The equivalent dipoles were located close to the sources of the early somatosensory evoked field component N20m, which suggests that the mu rhythm is generated mainly at the primary somatosensory hand projection area. The frequency spectrum of the mu had major peaks around 10 and 21 Hz in all subjects. The high-frequency activity was blocked by clenching of the fist, but not by opening of the eyes, in agreement with characteristics of the electric mu rhythm.
Adult↗
Interaural interaction in the human auditory cortex.
We studied the effect of binaural, contralateral and ipsilateral stimulation on middle- and long-latency auditory-evoked magnetic fields using trains of 40-Hz clicks. The stimuli evoked both a transient response (N100m) and a 40-Hz response, which presumably reflects coalescence of middle-latency responses. Binaural stimuli elicited significantly larger 40-Hz responses and sustained fields than contralateral stimuli. N100m amplitudes did not differ between binaural and contralateral stimulation; the dipole moments were even smaller to binaural than contralateral stimuli. Responses to the ipsilateral stimuli were always the smallest.
Acoustic Stimulation↗
Molecular characterization of a Y;15 translocation segregating in a family.
We have used Y-specific and Y-derived DNA probes for in situ hybridization and Southern blotting analysis to characterize a Y;15 translocation showing normal Mendelian inheritance in a family. Cytogenetically there appeared to be an unbalanced translocation of Yqh to 15p; this translocation may be considered as a prototype of those translocations between Yq and the short arm of an acrocentric chromosome which have a population incidence of approximately 1 in 2,000. Our molecular studies showed that, in all probability, the breakpoints were near the border between Yq11.23 and Yq12, and in 15p11, respectively; the translocation is abbreviated t(Y;15)(q12;p11). Using the Y-specific probe pY431 in a quantitative Southern hybridization assay, normal females had no hybridization, female carriers and normal men had the same amount, and male carriers had twice that amount. Cytogenetic analysis and quantitative in situ hybridization using probes pY431 and pY3.4 were consistent with the hypothesis that the portion of Yq translocated to 15p comprised all of Yq12 and none of Yq11. The absence of Southern hybridization with probes specific for Yp and Yq11 confirmed this observation. Even though the family was ascertained through two brothers who both had schizophrenia and were carriers of the translocation, the clinical evaluation of a total of nine individuals with the translocation and five without it did not suggest its association with an abnormal phenotype.
Chromosome Banding↗
Evoked responses of human auditory cortex may be enhanced by preceding stimuli.
We report enhancement of the 100 msec deflection N100m of the auditory evoked magnetic field in paired-stimulus paradigms. Noise bursts of 50 msec duration were delivered in pairs to the left ear at interpair intervals of 1.2-1.4 sec. Stimulus onset asynchrony (SOA) within the pair was either 70, 150, 230, 300, 370 or 500 msec, all intervals being presented randomly within the same block. Magnetic responses were recorded over the right hemisphere with a 7-channel first-order SQUID gradiometer. The mean amplitude of N100m to the second stimulus was maximal at an SOA of about 150 msec, decreasing at longer SOAs to an amplitude about equal to that of the N100m evoked by the first stimulus. Similar enhancement effects were elicited by noise bursts, square-wave tones and sinusoidal tones, by pauses in a continuous noise, and when the two stimuli of a pair were led to different ears.
Auditory Cortex↗
Early deflections of cerebral magnetic responses to median nerve stimulation.
We have recorded early components of somatosensory evoked magnetic fields with a sensitive 7-channel first-order gradiometer using a wide recording passband (0.05-2000 Hz) and high sampling frequency (8000 Hz). The left median nerve was stimulated at the wrist and responses were recorded over the right hemisphere. The responses typically consisted of a N20m peaking at 18-20 msec, a small P22m peaking at 21-23 msec and a P27m peaking at 29-31 msec. The topography of N20m could be explained by a tangential current dipole in the posterior wall of the central sulcus (probably in area 3b). The equivalent dipoles of P27m were located on average 10 mm antero-medially to the sources of N20m. This suggests that P27m may get a contribution from the anterior wall of the central sulcus. An increase of stimulus repetition rate from 2 to 5 Hz decreased the amplitude of P27m more than that of N20m, which implies that these two deflections are generated by different neural networks.
Adult↗