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Biomedical subjects

T Järvilehto

Publications and source records attributed to T Järvilehto.

At least 19 recordsLinked to original sources
PubMed1995

Frontal midline theta related to learning in a simulated driving task.

The occurrence of frontal midline theta activity (4-7 Hz) was studied in a simulated driving task during consecutive phases of goal-directed behaviour. Electrical activity of the forebrain (Fz) was analysed in a simulated traffic situation in which the subject had to find the correct way to drive a car through a set of roads in a computer game. The occurrence of theta activity was analysed during seven consecutive sections of the game. The results showed that the occurrence of theta activity increased during learning--successful behaviour produced more theta than unsuccessful behaviour. In some sections of the game the percentage of theta was larger than in others. It is suggested that the theta activity reflects relaxed concentration after mastering the game.

Adult↗
PubMed1993

Effect of ethanol on hippocampal neurons depends on their behavioural specialization.

Acute effect of ethanol on hippocampal neurons was studied during food acquisition behaviour in seven rabbits. The rabbits were taught to acquire food from a feeder by pressing a pedal on the same side of the cage. The behaviourally specialized units (L units related to newly learned behaviour and M units related to behaviour formed before learning, e.g. certain movements) were comparable with the 'place' (projectional pyramidal and granular cells) and 'displace' (non-pyramidal interneurons) units of the current classification. The same direction of ethanol effects was found as for the limbic cortex; the number of certain kinds of L units decreased and that of M units increased but there was no significant change in the relative number of L and M units as a whole. The background frequency of L units decreased, but the frequency within activations increased. The results confirm our earlier findings on the most marked depressive effect of ethanol on L units and show that it is the behavioural specialization, not the morphological unit type, which is a major determinant of the ethanol influence.

Animals↗
PubMed1991

Acute effects of alcohol on unit activity in the motor cortex of freely moving rabbits: comparison with the limbic cortex.

Unit activity was recorded from the motor cortex of eight freely moving rabbits in order to examine the acute effect of ethanol (1 g kg-1) on organization of unit activity and to compare it with our earlier results from the limbic cortex. The rabbits performed a food-acquisition task in the experimental cage. Unit activity was recorded during behaviour in the control experiment followed by the alcohol experiment on the next day. After ethanol, behavioural mistakes and the duration of the behavioural cycle significantly increased. In the control experiments activation of 58% of the units had no constant relation to the phases of the behavioural cycle (non-involved units), whereas 42% of the units were constantly activated during certain phases (involved units). Two per cent of the latter units were activated in relation to newly learned behavioural acts (e.g. pedal pressing; L units), 28% in relation to food seizure and/or grinding (S units) and 12% in relation to certain movements during different behavioural acts (M units). Ethanol had no effect on the number of active units and the same relation between the number of non-involved and involved units or between the number of different types of involved units was found. However, the number of involved units decreased in the upper and increased in the lower cortical layers. Also the number of units with low background frequency increased, although the frequency within activations did not change. In our earlier study the number of active units in the limbic cortex decreased after ethanol by one third and the relation between the number of L and M units was reversed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

The return of sensitivity to cold, warmth and pain from excessive heat in free microvascular flaps.

Recovery of sensitivity to cold, warmth and pain caused by excessive heat in various types of free microvascular flaps was studied psychophysically in 27 patients who had undergone such operations four months to four years earlier. A thermal stimulator based on the Peltier principle and controlled by a microprocessor was used to measure the sensitivity to temperature in the transplants. The results were compared with the measured thresholds in the opposite sites in corresponding normal body areas. The present study showed that sensitivity to cold, warmth, and pain caused by excessive heat did return to some free microvascular flaps. According to the measurements the sensation started to return after 6 months in some flaps, and all types of thermal stimuli were felt by one patient as early as 10 months after operation. The return was more pronounced in younger people and in smaller flaps. If the hands, feet, or head defects were reconstructed with a thin skin flap (posterior aspect of thigh, dorsum of foot, or subscapular) the recovery of sensitivity was verified. Sensation returned to the musculocutaneous and osteomusculocutaneous transfers if they were on the hands or the head, or if they were sutured to healthy tissue with normal sensation. The main advantage of the psychophysical sensory testing method that we used is that it gave exact numerical data that made it possible to compare results among the different patient groups and even those obtained at different clinics and laboratories.

Adolescent↗
PubMed1990

Acute effect of ethanol on the pattern of behavioural specialization of neurons in the limbic cortex of the freely moving rabbit.

Single-unit activity was studied in the limbic cortex of eight freely moving rabbits in order to find out what kind of changes in the organization of unit activity correlate with behavioural disturbances following an acute administration of ethanol (1 g kg-1). The rabbits were taught to acquire food by pressing pedals in the experimental cage. Unit activity was recorded during this behaviour in a control experiment and the alcohol experiment took place the next day. The number of behavioural mistakes significantly increased in the alcohol experiments. The pattern of behavioural specialization of the units also differed between the control and alcohol experiments. In the control experiments 55% of units did not show any constant activations in relation to the behavioural phases (non-involved units), 28% of the units were constantly activated in relation to one or more behavioural phases learned in the cage (e.g. use of pedals; L units) and 17% of units showed activations in relation to the behaviour learned before the teaching of food acquisition (e.g. movements in general; M units). In the alcohol experiments the number of active units decreased by one-third compared with that found in the control experiments. The relative number of non-involved units did not change, whereas the relation between L and M units was reversed (11% L units and 34% M units). This was the result of a decrease in the number of active L units, mainly in the upper layers of the cortex. The results indicate that ethanol has a selective depressing effect on cortical neurons with different behavioural specialization, which could explain the behavioural disturbances observed in the alcohol experiments.

Animals↗
PubMed1989

Regeneration of cold, warmth and heat-pain sensibility in human skin grafts.

Recovery of cold, warmth and heat-pain sensations in skin grafts was studied psychophysically in 22 patients who had had split skin grafts transplanted over muscle fascia 1 to 4 years earlier. A thermal stimulator based on the Peltier principle and controlled by a microprocessor was used to measure the thermal sensitivity of the grafts. Control measurements were obtained from the corresponding opposite side of the body. Cold sensitivity was present in 14 grafts (from 1-4 years old). However, with one exception, the threshold for cold sensation remained higher than normal in all patients. Warmth sensitivity was present in 6 grafts (from 1-4 years) which were all also sensitive to cold. Heat-pain sensitivity was present in 8 grafts. If the warmth and heat-pain sensibility had recovered, the sensation threshold was closer to the normal value than that for cold. In 7 grafts (from 1-3 years) no recovery was obtained.

Adult↗
PubMed1986

Response characteristics of peripheral mechanoreceptive units in man: relation to the sensation magnitude and to the subject's task.

The characteristics of responses of 23 peripheral mechanoreceptive units to tactile pulses of varying amplitude (50-950 micron) were studied by means of human microneurography during two different tasks. The simultaneously recorded unit responses were related to estimates of sensation magnitude in order to study the coding properties of units. The possible effects of the tasks were studied by comparing the response to identical stimulus pulses during the two tasks. The S-R functions of single units had smaller exponents than the magnitude estimation functions, but the relation between the number of impulses/frequency of impulses and the simultaneously given magnitude estimate was well described by linear functions for 74% of units. Thus both of these parameters may serve as codes for stimulus amplitude. For 18 units differences were obtained between the two task situations when thresholds, latency of the first impulse, mean frequency of impulses, or number of impulses in responses were compared. The differences were partly due to a continuous decrease of sensitivity of units with time. However, the results indicate also that the sensitivity of the units was higher during the magnitude estimation than during the counting task. The effect of the task of the subject on the sensitivity of the peripheral mechanoreceptive units may be mediated through direct neural connections. The results indicate that the reorganization of the neural processes according to the task of the subject is not limited to the central nervous system, but involves also the periphery.

Acoustic Stimulation↗
PubMed1985

Vibrotactile atonal interval correlated with activity in peripheral mechanoreceptive units innervating the human hand.

The quality of sensations and the vibrotactile atonal interval-the gap between detection and vibration thresholds-were studied with vibratory stimuli of varying frequency (20, 80 and 160 Hz) and duration (100, 400 and 800 ms) applied to the hairy and glabrous skin of the hand. Detection and vibration thresholds were also determined while simultaneously recording single unit activity from the radial nerve innervating the hairy skin of the hand. Both thresholds were lower on the glabrous than the hairy skin, and the thresholds decreased on both skin areas with increasing vibration frequency. A sensation of short duration was elicited at detection threshold only with a 20-Hz stimulus of 100-ms duration; with other frequency-duration combinations sensations of longer duration were reported. Considerably larger vibration amplitudes were needed on both skin areas for the sensations to be unequivocal with respect to duration and pitch (vibration threshold). There was no significant effect of stimulus duration on vibrotactile thresholds. The width of the average atonal intervals was above 10 dB on both skin areas, and with increasing vibration frequency, decreasing values of atonal intervals were obtained on the hairy skin, whereas considerably increasing values were obtained on the glabrous skin. Recording of single unit activity indicates that on the hairy skin detection of the stimulus at 20 Hz is correlated with activation of slowly adapting (SA) type II and the most sensitive rapidly adapting (RA) units, while distinct vibratory sensations involve entrainment of RA units. Also at 80 Hz, non-pacinian units could contribute to the mechanism of vibrotactile thresholds, whereas at 160 Hz only pacinian (PC) units are involved.

Adaptation, Physiological↗
PubMed1985

Auditory and visual evoked potentials of schoolboys with spelling disabilities.

EEG evoked potentials were studied in 23 young adolescent poor spellers and 21 controls. Findings typical of poor spellers were long auditory evoked potential (AEP) latencies and low amplitudes of early AEP deflections. A high frequency of spelling errors concerning the word as a whole was associated with low AEP P50 and P300 amplitudes. Poor reading was associated with high AEP sustained potential amplitudes and a long AEP P185 latency. Generally, poor spellers seem to have problems with the early filtering processes of of attention, whereas spelling errors concerning the word as a whole seem to be associated with problems of late attentional processes. The abnormal findings in the poor spellers are interpreted in terms of a brain maturational delay that presents as an attentional disorder.

Adolescent↗
PubMed1983

Somatosensory evoked potentials associated with tactile stimulation at detection threshold in man.

Somatosensory evoked potentials elicited by sub- and supraliminal tactile pulses were studied during continuous threshold measurement. Two threshold methods were used: a modified tracking method and a detection method. With both methods threshold estimates of the same order of magnitude were obtained. Stimuli just above the threshold elicited a distinct somatosensory evoked potential with components P50, P100, N190 and P400. No such SEP was associated with the subliminal stimuli. However, in some cases some potential oscillations were obtained, time-locked to the subliminal stimuli; these are suggested to be due to errors in responding. In control experiments detected stimuli elicited a distinct SEP, but no SEP was associated with undetected stimuli of identical amplitude. The results indicate that in the psychophysical threshold determination the neural processing reflected in the SEP is associated only with supraliminal tactile stimulation. The lack of evoked brain activity associated with subliminal tactile stimuli supports the hypothesis derived from human microneurographic studies, stating that the tactile detection threshold may be based on an extremely small peripheral input, perhaps only on a single impulse in a single peripheral fiber.

Adult↗
PubMed1982

Paradoxical heat sensations during moderate cooling of the skin.

Paradoxical heat sensations during cooling of the skin were examined in two experiments. In Expt. I the number of occurrences of sensation was studied in 19 naive test subjects (Ss) when cooling from thermal indifference both without and with preceding heating. Without preceding heating 13 Ss reported sensations of paradoxical heat (9.8% of all stimulations). Preheating markedly facilitated the occurrence of the sensations (35% of all stimulations). In Expt. II the effects of cooling velocity (velocities 0.4, 0.7 and 2.0 degrees C/s) and the type of skin area stimulated (hairy or glabrous skin of the hand) on the thresholds of paradoxical sensations were studied in 4 Ss without and with preheating. Cooling velocity, type of skin area and preheating had significant effects on the sensation thresholds, the thresholds being the higher (i.e. the sensation appearing at lower stimulation temperatures) the higher the cooling velocity, if the stimuli were applied to the glabrous skin, or if no preheating was used. The results confirm the existence of paradoxical heat sensations during cooling of the skin and suggest that the sensation is mediated by polymodal units supplied by C-fibers.

Adult↗
PubMed1981

Peripheral neural basis of tactile sensations in man: I. Effect of frequency and probe area on sensations elicited by single mechanical pulses on hairy and glabrous skin of the hand.

Tactile thresholds and sensation magnitudes for single mechanical pulses of varying frequency and probe area were studied in order to provide psychophysical data for correlations of tactile sensations with functional properties of different types of human peripheral nerve fibers. Single mechanical pulses were delivered to the hairy or glabrous skin of the hand by means of a perspex probe (area 0.07, 0.7, 3.1, or 12.5 sq.-mm) fixed to the moving coil of an electromechanical vibrator. The frequency of the single pulse was 20, 60 or 150 HZ. Absolute and touch thresholds were measured with a method of production. Suprathreshold sensations were measured with the method of magnitude estimation (6 predetermined displacement amplitudes ranging from 50 to 950 micrometers). Both absolute and touch thresholds were significantly higher on the hairy than on the glabrous skin. The absolute thresholds varied between 44 and 140 micrometers on the hairy and between 9 and 45 micrometers on the glabrous skin; the touch threshold varied between 75 and 300 micrometers and 24 and 153 micrometers, respectively. Lower threshold values were obtained on both skin areas with increasing frequency of the pulse and probe area, the latter effect being significant only for the hairy skin. Standardized magnitude estimation functions could be described with power functions on both skin areas, the exponents of the functions varying between 0.70 and 1.41 on the hairy and between 0.55 and 0.86 on the glabrous skin. The equi-sensation contours showed the difference of sensitivity between the skin areas. Larger sensation magnitudes were obtained with increasing frequency of the pulse and probe area on both skin areas. These psychophysical findings indicate that there is a functional difference at absolute sensation thresholds between hairy and glabrous skin. This difference, however, disappears at higher sensation levels.

Adult↗
PubMed1981

Peripheral neural basis of tactile sensations in man: II. Characteristics of human mechanoreceptors in the hairy skin and correlations of their activity with tactile sensations.

Properties of the human mechanoreceptors in the hairy skin of the back of the hand were studied by microelectrode measurements from the radial nerve. Correlations of unit activity with sensations elicited by tactile pulses (single cycle sinusoids of 20, 60 and 150 HZ) were examined with simultaneous measurements of unit activity and sensation thresholds and magnitude. A total of 264 mechanoreceptive units were identified. Of all units 66% were classified as slowly adapting (SA) and 34% as rapidly adapting (RA) units. Mechanical thresholds of the units as well as simultaneously measured sensation thresholds decreased with increasing frequency of the pulse. The thresholds of several SA units were identical with the subjective thresholds. The responses of the units to supraliminal pulses consisted maximally of 7 impulses. Most SAI and RA units were able to code to some extent the stimulus amplitude on the basis of number of impulses, but only RA units had stimulus-response functions indicating velocity coding. Comparisons of the estimates of sensation magnitude with the number of impulses in the response indicated that the estimate may be based mainly on activity in a population of RA units. The comparison of the present results with earlier reports on properties of receptors in the glabrous skin of the human hand indicates that there are some differences between the characteristics of receptors in the hairy and glabrous skin. However, human receptors in the hairy skin do not seem to differ from the corresponding receptors in the animals.

Adult↗
PubMed1979

Auditory evoked transient and sustained potentials in the human EEG: I. Effects of expectation of stimuli.

The characteristics of auditory evoked transient and sustained potentials were recorded using trains of four-tone stimuli of 1-second duration (interstimulus interval = 1 second) presented once every minute. The subject either attentively expected the stimuli or ignored them while reading. The electroencephalogram was recorded from derivations Cz-Al and Fz-Al. Expectation of the stimuli was associated with increased amplitudes of the transient responses both at the first stimulus of the train and during stimulus repetition. In contrast, the sustained potential at the first stimulus of the train was unchanged or smaller when the subject expected the stimuli. During stimulus repetition, however, the amplitude of the potential was enhanced by expectation of the stimuli. The results support the hypothesis of two sustained potential components and stress the importance of stimulus repetition rate when sustained potentials are studied.

Acoustic Stimulation↗
PubMed1979

Auditory evoked transient and sustained potentials in the human EEG: II. Effects of small doses of ethanol.

The effect of small doses of ethanol (0.4 g/kg) on auditory evoked transient and sustained potentials was studied. Tones of 1-second duration were presented in trains of four stimuli (interstimulus interval = 1 second; intertrain interval = 1 minute). The electroencephalogram was recorded from derivation Cz-Al. Ethanol depressed the transient responses both at the first stimulus of the train and during repeated stimuli. The sustained potentials elicited by the first stimuli of the train were not affected by ethanol, whereas the sustained potentials elicited by repeated stimuli were larger in amplitude under the influence of ethanol than during control experiments. It is suggested that the decrease of the transient responses under the influence of ethanol is mainly due to depression of the reticular formation, whereas the increase of sustained potentials reflects ethanol-induced release of intracortical inhibition.

Acoustic Stimulation↗
PubMed1978

Effect of stimulus repetition on negative sustained potentials elicited by auditory and visual stimuli in the human EEG.

Effect of repetition of auditory and visual stimuli on sensory-evoked sustained potentials was studied. The stimuli were tones and flashes of 1 sec duration presented in trains of six stimuli with an inter-stimulus-interval of 1 sec. The repetition rate of the trains was 1 train/min. The EEG was recorded from electrodes located at Cz, Pz and Oz. Both auditory and visual stimuli elicited negative sustained potentials which during the first stimuli of the trains were maximal in amplitude and shortest in latency at Cz. Repetition of the stimulus resulted in almost complete disappearance of the sustained potentials; for auditory stimulation a small negative shift was recorded only at Cz, whereas for visual stimulation a small sustained potential was seen only at Pz and Oz. The results indicate that the slow potentials evoked by short tones or lights are composed of at least two components. One of these components may reflect neural processing associated with orienting reflex. The other component seems to be related to specific neural processing of the stimulus.

Acoustic Stimulation↗