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Biomedical subjects

H Tiitinen

Publications and source records attributed to H Tiitinen.

53 records · Page 3Linked to original sources
PubMed1993

Attention and mismatch negativity.

The mismatch negativity (MMN) component of the auditory event-related potential (ERP) is elicited by infrequent, physically deviant stimuli in a sequence of frequent homogeneous stimuli (standards). It has been suggested that the MMN is generated by an automatic (attention-independent) neural mismatch process with a memory trace that encodes the physical features of the standard stimulus. The proposed MMN independence of attention was addressed in the present study. Standard stimuli and two types of deviant stimuli, differing from standards either in frequency or intensity, were dichotically presented in random order and at a rapid rate. The subject attended either to left- or right-ear stimuli, counting the number of a designated type of deviants in that ear. In the present conditions of very strongly focused attention, the MMN was elicited even by frequency change in the ignored input stream, and its amplitude was very similar to that of the MMN elicited by equivalent deviant stimuli (targets) in the attended input stream. In contrast, the MMN to intensity deviation was clearly attenuated in the absence of attention. This effect is, however, probably due to the attention effect on the MMN generator itself rather than the antecedent sensory-analysis and -storing functions.

Acoustic Stimulation↗
PubMed1993

Tonotopic auditory cortex and the magnetoencephalographic (MEG) equivalent of the mismatch negativity.

Two tone stimuli, one frequent (standard) and the other infrequent (a slightly higher, deviant tone), were presented in random order and at short intervals to subjects reading texts they had selected. In different blocks, standards were either 250, 1,000, or 4,000 Hz, with the deviants always being 10% higher in frequency than the standards of the same blocks. Magnetic responses elicited by the standard and deviant tones included N1m, the magnetoencephalographic equivalent of the electrical N1 (its supratemporal component). In addition, deviant stimuli elicited MMNm, the magnetic equivalent of the electrical mismatch negativity, MMN. The equivalent dipole sources of the two responses were located in supratemporal auditory cortex, with the MMNm source being anterior to that of N1m. The dipole orientations of both sources in teh sagittal plane depended on stimulus frequency, suggesting that the responses are generated by tonotopically organized neuronal populations. The tonotopy reflected by the frequency dependence of the MMNm source might be that of the neural trace system underlying frequency representation of auditory stimuli in sensory memory.

Acoustic Stimulation↗
PubMed1982

Cellular immunity during follow-up of patients with sarcoidosis of varying duration.

Cellular immunity was followed up at 3 month intervals for 1 year in 43 patients with sarcoidosis representing three well defined categories of the disease viz acute (12), subacute (20) and chronic (11). Twelve apparently healthy individuals served as controls. Each follow-up included the following tests: total number of blood lymphocytes, T cells, B cells, leucocyte migration tests with PPD, BCG and Kveim test material and stimulation tests of lymphocytes in vitro in the presence of PHA, Con A, PPD and PWM. Statistically, the most abnormal initial findings in all the tests were noted in acute sarcoidosis, followed by the subacute group. The acute group showed the most marked changes also during the follow-up. The smallest changes during the follow-up were seen in the patients with the chronic form of the disease. However, the inter-individual variation was considerable and no definite conclusions could be drawn from findings in a given case. Alterations in cellular immunity occur in sarcoidosis. They differ between different subgroups of patients and vary differently in course of time. Well defined criteria for inclusion of patients in an investigation and repeated studies of included patients will increase the information available from investigations of cellular immunity in sarcoidosis.

Acute Disease↗
PubMedDate not supplied

Frequency change detection in human auditory cortex.

We offer a model of how human cortex detects changes in the auditory environment. Auditory change detection has recently been the object of intense investigation via the mismatch negativity (MMN). MMN is a preattentive response to sudden changes in stimulation, measured noninvasively in the electroencephalogram (EEG) and the magnetoencephalogram (MEG). It is elicited in the oddball paradigm, where infrequent deviant tones intersperse a series of repetitive standard tones. However, little apart from the participation of tonotopically organized auditory cortex is known about the neural mechanisms underlying change detection and the MMN. In the present study, we investigate how poststimulus inhibition might account for MMN and compare the effects of adaptation with those of lateral inhibition in a model describing tonotopically organized cortex. To test the predictions of our model, we performed MEG and EEG measurements on human subjects and used both small- (<1/3 octave) and large- (>5 octaves) frequency differences between the standard and deviant tones. The experimental results bear out the prediction that MMN is due to both adaptation and lateral inhibition. Finally, we suggest that MMN might serve as a probe of what stimulus features are mapped by human auditory cortex.

Adaptation, Physiological↗
PubMedDate not supplied

Aspiration biopsy of the spleen in patients with sarcoidosis.

Fine-needle aspiration biopsy of the spleen was performed on 101 patients with suggested sarcoidosis; it was the final diagnosis in 79. Adequate specimens were obtained in all cases with a 0.8 X 80 mm or 0.7 X 40 mm disposable needle. Fine-needle biopsy specimens of the spleen showed a granulomatous reaction in 19 out of the 79 cases with sarcoidosis (24%). There were three minor biopsy complications that required no treatment.

Biopsy, Needle↗