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Biomedical subjects

K Reinikainen

Publications and source records attributed to K Reinikainen.

At least 73 records · Page 4Linked to original sources
PubMed1987

Brain mechanism of selective listening reflected by event-related potentials.

Stimulus selection during selective listening on the basis of simple physical stimulus features is reflected by an event-related potential (ERP) component called the processing negativity (PN). PN has been proposed to indicate a matching or comparison process between the physical features of the stimulus and an 'attentional trace,' an actively formed and maintained temporary neuronal representation of the features defining the relevant stimuli. According to this theory, the smaller is the difference between the eliciting stimulus and that represented by the attentional trace, the longer time is the stimulus processed, and thus the larger in amplitude and longer in duration is the PN elicited. The relevant stimuli, perfectly matching with the attentional trace, and therefore eliciting the largest and longest-duration PN, are selected for further processing. In the present study, the relevant and irrelevant stimuli differed in pitch, and the magnitude of this pitch separation was varied between different stimulus blocks. The results support the afore-mentioned matching or comparison hypothesis of selective attention by showing that PN is not elicited only by the relevant stimuli but even by irrelevant stimuli, and further that the latter PN is larger in amplitude and longer in duration the more similar the irrelevant stimuli are to the relevant stimuli. This PN, however, was smaller than that to the relevant stimuli even for very small separations, reflecting high accuracy of the discrimination function of the attentional trace mechanism proposed to underly selective listening. The termination of the PN to the irrelevant stimuli was followed by a positivity which thus partly explained the difference (Nd) between the ERPs to the relevant and irrelevant stimuli.

Adult↗
PubMed1987

Stimulus selection during auditory spatial attention as expressed by event-related potentials.

Selective listening to stimuli with certain physical features, such as pitch or location, is reflected by an event-related brain-potential (ERP) component called the processing negativity (PN). PN may reflect a matching or comparison process between the sensory inflow and the hypothesized 'attentional trace'. The latter is an actively formed and maintained neuronal representation of the physical features defining the relevant stimulus. According to this matching theory of selective attention, the better the sensory input corresponds to the attentional trace the longer the stimulus is processes (as reflected by a larger and longer PN). This theory is supported by the experiment in which the relevant and irrelevant stimuli were separated from one another in pitch. It was found that even the irrelevant stimuli elicited PN, and further that this PN was larger the smaller the pitch separation between the eliciting stimuli and the relevant stimuli. The largest PN was elicited by the relevant stimuli. The present study finds analogous results when the relevant and irrelevant stimuli are separated in spatial origin rather than in pitch.

Adult↗
PubMed1987

Dementia without cholinergic deficit.

We examined the role of cholinergic system in multi-infarct dementia (MID) by measuring acetylcholinesterase (AChE) activities in cerebrospinal fluid (CSF) of clinically diagnosed MID patients, Alzheimer's disease (AD) patients and controls. In spite of the similar clinical severity of dementia, MID patients had unaltered AChE levels, whereas AD patients had significantly reduced AChE levels in CSF when compared to controls. In the autopsy study we analyzed choline acetyltransferase (ChAT) levels in four cortical brain areas from clinically and neuropathologically studied AD patients, demented non-AD patients and controls. ChAT activities in the cerebral cortex in non-AD patients were on the same level as in controls, but AD patients had a marked loss of ChAT activity in all four cortical brain areas studied. Although cholinergic deficit is a usual phenomenon associated with cognitive failure, severe dementia can exist without cholinergic dysfunction.

Acetylcholinesterase↗
PubMed1985

Cerebral neuromagnetic responses evoked by short auditory stimuli.

We presented 30 msec sinusoidal tone bursts to the subject's left ear once every 1300 msec. The number of standard tones (1000 Hz) between deviants (1030 Hz) varied randomly from 3 to 15 (even distribution) so that the probability of the standards was 0.9 and that of the deviants 0.1. During stimulation the subject was reading a book. Magnetic responses to the standards and deviants were measured at the estimated ends of the sylvian fissure and electrical responses at Fpz, Fz and Cz. In addition, extensive field maps over the right hemisphere were made from 60 to 75 points in 3 subjects. A least-squares fit was performed to find out the parameters of the equivalent current dipole in a spherically symmetrical head model. Field maps suggested that the source of magnetic response at 100 msec (N100m) can be approximated by a current dipole at the supratemporal plane, possibly at the primary auditory cortex. In two subjects the location and/or the orientation of the equivalent dipole changed during N100m, possibly due to change in the size of the activated cortical area. The deviant stimuli elicited in addition to N100m a second deflection, MMNm, peaking at about 200 msec. This response was regarded as specific to stimulus change. On the basis of field maps it was also concluded that MMNm got a contribution from activity at the supratemporal plane.

Adult↗
PubMed1984

The activation of unmyelinated or myelinated afferent fibers by brief infrared laser pulses varies with skin type.

Brief infrared laser pulses were applied to 3 different skin areas in man. Reaction times indicated that A delta-fibers were activated in the dorsal and volar skin of the finger whereas only C-fibers were activated in the hairy skin of the forearm. The qualitative sensations were in line with this interpretation. We conclude that the activation of unmyelinated or myelinated afferent fiber populations with brief laser pulses varies with skin type.

Adult↗
PubMed1984

Quantification of a number of biogenic amines and their metabolites in brain homogenates by gas chromatography--mass spectrometry.

A sensitive method is described for the assay of various biogenic amines and their metabolites from brain tissue homogenates. Based on gas chromatography-mass spectrometry and selected ion monitoring, the method allows reliable low-level quantification of the compounds of interest. By careful study of reaction conditions both in the preparation of derivatives for gas chromatography and in the synthesis of deuterated analogues for internal standard use, relatively simple procedures could be applied with good analytical efficiency. Correlation of the results with those obtained by a high-performance liquid chromatographic procedure was also investigated, and a neurologic application of the method is briefly discussed.

Alzheimer Disease↗
PubMed1984

Somatosensory evoked cerebral magnetic fields from SI and SII in man.

We have recorded cerebral magnetic fields elicited by electrical stimulation of median and peroneal nerves. Field mapping indicates that the deflections at 30-80 and 150-180 msec are due to activity at SI. Additional activity at 90-125 msec is generated at SII, on the superior bank of the sylvian fissure. At SI, the source locations are in agreement with the known somatotopy. Only contralateral stimuli evoke responses at SI, whereas both ipsi- and contralateral stimuli elicit responses at SII.

Adult↗
PubMed1984

A four-channel SQUID magnetometer for brain research.

A 4-channel differential SQUID magnetometer has been built. Its design principles and construction are described. Proper matching of the detection coil to the SQUID input is discussed. Examples of auditory, dental pain and visual evoked response data are presented.

Electroencephalography↗
PubMed1983

Neuromagnetic localization of cortical activity evoked by painful dental stimulation in man.

We have recorded cerebral magnetic fields evoked by painful dental stimulation. The field pattern indicates a current source at the upper bank of the anterior Sylvian Fissure, corresponding to the anterior end of the secondary somatosensory cortex. This finding suggests cortical representation of tooth pulp in man. The neuromagnetic technique, allowing the investigation of this cortical area, thus provides a new non-invasive tool for pain research.

Adult↗
PubMed1983

Neuromagnetic responses from the second somatosensory cortex in man.

Cerebral magnetic fields elicited by electric stimulation of peripheral nerves were studied in man. Responses were found over the Sylvian fissure at latencies of 95-125 ms for both contra- and ipsilateral stimuli. The field distribution indicated that the responses are generated in the second somatosensory cortex SII at the upper bank of the Sylvian fissure. These responses seem to provide the first non-invasive tool to study the function of SII in man.

Adult↗
PubMedDate not supplied

Selegiline treatment and the extent of degenerative changes in brain tissue of patients with Alzheimer's disease.

BACKGROUND: A beneficial effect of selegiline (L-deprenyl) in Alzheimer's disease (AD) has been reported in several clinical studies. METHODS: The brain tissue from 17 deceased patients, members of a double-blind clinical trial to assess the potential benefit of selegiline in AD, were analysed. FINDINGS: In our study, the decrease in the Mini-Mental State Examination (MMSE) scores during the progress of the disease had been significantly influenced by selegiline treatment. Prior to death, the MMSE scores were significantly higher in those patients receiving selegiline than in those receiving placebo. However, according to our results, none of the lesions critical for AD diagnosis, such as counts of senile/neuritic plaques, neurofibrillary tangles or beta-A4 load, were influenced by the selegiline treatment. INTERPRETATION: In conclusion, according to our study, mechanisms other than neuronal degeneration seen as lesions critical for AD diagnosis are influenced by selegiline treatment, leading to the functional benefit found in AD.

Aged↗
PubMedDate not supplied

Mismatch negativity (MMN) for sequences of auditory and visual stimuli: evidence for a mechanism specific to the auditory modality.

ERPs to sequences of standard and deviant sinusoidal 100 msec tone pips, high-contrast sinusoidal gratings and to their simultaneously presented combinations were recorded. Mismatch negativity (MMN), an ERP component elicited by deviant stimuli, was estimated for the different stimulus sequences in order to find out whether it reflects modality-specific processes or non-specific attentive phenomena. In addition to the auditory modality, we studied whether the mismatch response could be evoked by a deviant visual stimulus in a visual sequence or by a deviant stimulus in either modality. The results show that only auditory stimuli produced the mismatch response, suggesting that MMN is not a manifestation of a general attentional mechanism but is probably specific to the auditory modality.

Acoustic Stimulation↗