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J Knuutila

Publications and source records attributed to J Knuutila.

11 recordsLinked to original sources
PubMed1996

Processing of complex sounds in the human auditory cortex as revealed by magnetic brain responses.

Processing of simple and complex sounds in the human brain was compared by recording extracranial magnetic mismatch responses (MMNm; the magnetic counterpart of the mismatch negativity, or MMN) to frequency changes in these sounds. Generator sources, modeled as equivalent current dipoles (ECDs), of MMNm responses to a change in one frequency element of complex sounds (a chord and a serial tone pattern) were located in supratemporal auditory cortex, on average, 10 mm medially to the source of an MMNm elicited by an identical frequency change in a simple tone. These results suggest that at least partially different supratemporal neuron populations are involved in processing changes in simple and complex sounds and that sensory-memory representations for these sounds may be located in different fields of the auditory cortex.

Adult↗
PubMed1995

Bilateral activation of the human somatomotor cortex by distal hand movements.

We recorded cortical magnetic signals, simultaneously over the whole scalp, from 6 healthy subjects during 3 motor tasks to track the varying proportion of contra- vs. ipsilateral activation. The subjects performed self-paced index finger flexions, simultaneous flexion of 4 fingers, and a sequence of rapid digit movements in different sessions. Index finger and 4-finger movements were associated with phasic bilateral dampening of spontaneous 10 and 20 Hz rhythms along the central sulcus, starting approximately 1 sec before the movement in the contralateral hemisphere. A rebound occurred within 1 sec after the index finger and 4-finger flexions; the rapid finger movements resulted in a persistent blocking of the rhythms. Averaging with respect to movement onset showed a slow bilateral frontal readiness field starting about 0.5 sec prior to motion onset. It was followed, within 200 msec after movement onset, by phasic movement-evoked fields (MEFs) which were bilateral during the tasks involving several fingers. The contra- vs. ipsilateral MEF amplitude ratio C/I decreased from 4.0 during index finger movements to 0.6 during rapid finger flexions, reflecting the enhanced activation of the ipsilateral primary somatomotor cortex with increasing complexity of movement.

Adult↗
PubMed1994

Activation of the human posterior parietal cortex by median nerve stimulation.

We recorded somatosensory evoked magnetic fields from ten healthy, right-handed subjects with a 122-channel whole-scalp SQUID magnetometer. The stimuli, exceeding the motor threshold, were delivered alternately to the left and right median nerves at the wrists, with interstimulus intervals of 1, 3, and 5 s. The first responses, peaking around 20 and 35 ms, were explained by activation of the contralateral primary somatosensory cortex (SI) hand area. All subjects showed additional deflections which peaked after 85 ms; the source locations agreed with the sites of the secondary somatosensory cortices (SII) in both hemispheres. The SII responses were typically stronger in the left than the right hemisphere. All subjects had an additional source, not previously reported in human evoked response data, in the contralateral parietal cortex. This source was posterior and medial to the SI hand area, and evidently in the wall of the postcentral sulcus. It was most active at 70-110 ms.

Adult↗
PubMed1993

Parietal epileptic mirror focus detected with a whole-head neuromagnetometer.

Whole-head magnetoencephalographic recordings revealed two parietal epileptic foci in homotopic areas of the hemispheres. The discharges occurred 17-20 ms later on the left than on the right hemisphere, implying the existence of a left-sided mirror focus. The foci were about 1 cm posterior to the hand primary somatosensory area, identified by evoked response measurements, and thus suggested epileptic activity at the parietal association cortex, in agreement with the observed callosal conduction time.

Adolescent↗
PubMed1993

Interaction between representations of different features of auditory sensory memory.

The neurophysiological basis of sensory memory was studied by measuring the magnetic counterpart (MMNm) of the mismatch negativity (MMN) with a whole-head 122-channel magnetometer. The MMNm is a response to a difference in the presented stimulus and a neuronal memory trace formed by repeated standard stimuli. This trace must contain information about the feature differing in the deviant. Keeping one feature (frequency) constant, we studied how other stimulus features affect the strength of the MMNm. The MMNm to a frequency change was weaker when the other features varied than when they were constant. This suggests that the MMNm to a frequency change is not independent of other stimulus features.

Acoustic Stimulation↗
PubMed1993

Functional organization of the human first and second somatosensory cortices: a neuromagnetic study.

Multichannel neuromagnetic recordings were used to differentiate signals from the human first (SI) and second (SII) somatosensory cortices and to define representations of body surface in them. The responses from contralateral SI, peaking at 20-40 ms, arose mainly from area 3b, where representations of the leg, hand, fingers, lips and tongue agreed with earlier animal studies and with neurosurgical stimulations and recordings on convexial cortex in man. Representations of the five fingers were limited to a cortical strip of approximately 2 cm in length. Responses from SII peaked 100-140 ms after contra- and ipsilateral stimuli and varied considerably from one subject to another. Signs of somatotopical organization were seen also in SII. Responses of SII were not fully recovered at interstimulus intervals of 8 s.

Acoustic Stimulation↗
PubMed1993

Memory-related processing of complex sound patterns in human auditory cortex: a MEG study.

Responses of the human brain to a complex sound pattern were recorded with a 24 channel magnetometer. The sound pattern consisted of 9 successive 50 ms segments, each with a different frequency. An infrequent change in the frequency of one of the segments elicited a magnetic mismatch response (MMNm) which peaked at about 200 ms after the deviant segment onset and resembled the electrical mismatch negativity (MMN). The equivalent current dipole which best explained the MMNm was located in the supratemporal auditory cortex, suggesting that a memory trace for the sound pattern was stored in that region.

Adult↗
PubMed1992

Cortical somatosensory magnetic responses in multiple sclerosis.

Somatosensory evoked magnetic fields (SEFs) to contralateral median and ulnar nerve stimulation were analyzed in 10 patients with multiple sclerosis and in 8 healthy controls. SEFs were recorded with a 24-channel SQUID gradiometer over both hemispheres. Seven patients showed abnormally large-amplitude SEF deflections at 60-80 msec; 5 of them had multiple lesions around lateral ventricles in magnetic resonance imaging. In 2 patients with plaques at the level of 3rd and 4th ventricles and medulla, the 30 msec responses were enlarged. The equivalent sources of 20 msec and 30-80 msec responses were in the primary hand sensorimotor cortex both in patients and in control subjects. The results suggest that early and middle-latency SEFs reflect parallel processing of somatosensory input. Recording of middle-latency evoked responses, electric or magnetic, may give additional information about the somatosensory function in multiple sclerosis.

Adult↗
PubMed1992

Generator sites of spontaneous MEG activity during sleep.

We have recorded spontaneous magnetoencephalographic (MEG) activity during overnight natural sleep in 4 healthy adults with a 24-channel SQUID gradiometer, mainly over the sides of the head. All sleep stages were obtained. The MEG wave forms resembled the EEG phenomena recorded simultaneously from the scalp midline, but the electric and magnetic signals did not always coincide. The source locations of different signals were studied by using a current dipole model. The equivalent sources of magnetic transients, resembling and often coinciding with the electric vertex waves and K-complexes, as well as the transients during REM sleep, were concentrated within a volume of 4 x 4 x 3 cm3 in the inferior parietal lobe. For spindles and slow waves, no such focal generators were found.

Adult↗
PubMed1988

Neuromagnetic responses from a deaf subject to stimuli presented through a multichannel cochlear prosthesis.

Neuromagnetic responses to stimuli presented through a 4-channel cochlear prosthesis were recorded from a deaf subject. The topography of the responses agreed with activation of the supratemporal auditory cortex. The responses to tone pips, noise/square-wave sequences, and to intermittent frequency modulation of a continuous tone resembled those obtained from subjects with normal hearing, being consistent with the good performance of this subject with his implant.

Acoustic Stimulation↗