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I M Tarkka

Publications and source records attributed to I M Tarkka.

35 records · Page 2Linked to original sources
PubMed1991

Topography of scalp-recorded motor potentials in human finger movements.

Four distinct negative events were identified in the averaged, scalp-recorded EEGs of normal subjects before and after the onset of self-paced, voluntary finger movements; reaction-time movements and passive movements were also studied. These events are the peak of the negative slope (NS'), the initial slope of motor potential (isMP), the parietal peak of motor potential (ppMP), and the frontal peak of motor potential (fpMP). For self-paced movements, NS' and isMP occurred before the onset of electromyographic (EMG) activity, and ppMP and fpMP occurred after the onset of EMG activity. NS' had a wide distribution, covering the parietal region with slight contralateral predominance. The isMP mapped focally over the contralateral hand motor area on the scalp. The location of ppMP was similar to that of isMP. The fpMP was localized anterior and medial to motor cortex with a contralateral preponderance and possible location over the supplementary motor area. The isMP and fpMP also were identified in the recordings of reaction-time movements, but only the fpMP persisted in the recordings of passive movements. The isMP appears to reflect activation of the cortical cells in the hand area of motor cortex for the execution of voluntary movement, and the fpMP appears to reflect proprioceptive feedback from the periphery.

Adult↗
PubMed1990

Topography of movement-related cortical potentials is abnormal in Parkinson's disease.

We studied the scalp-recorded, movement-related cortical potentials occurring immediately before and after the onset of movement in 5 patients with asymmetric Parkinson's disease. The topographic distribution of the initial slope of motor potential (isMP) was diffuse for voluntary finger movements of the more affected hand but normal for movements of the less affected hand. The frontal peak of motor potential (fpMP) was located more posterior in patients than in normal subjects. The peak amplitudes of the potentials were normal in all patients. The topographic abnormalities might reflect inadequate excitatory activity from the basal ganglia to the primary motor cortex and the supplementary motor area.

Adult↗
PubMed1990

Cortical topography of premotor and motor potentials preceding self-paced, voluntary movement of dominant and non-dominant hands.

The cortical potentials preceding movement, negative slope (NS'), premovement positivity (PMP), and the initial slope of motor potential (MP), were studied in detail with a 29-channel averaged EEG mapping technique in normal subjects. Self-paced, voluntary movements of the right and left index fingers were performed up to 150 times, and topographic color maps were created from the averaged wave forms. The maps revealed NS' of the dominant hand on the vertex and NS' of the non-dominant hand on the contralateral centroparietal area. PMP appeared on the ipsilateral precentral area, and the initial slope of MP appeared on a small, distinct contralateral precentral area, presumably the hand motor area. The amplitudes of the potentials did not show significant differences between dominant and non-dominant hands. PMP and the initial slope of MP appeared significantly earlier preceding non-dominant hand movement as compared with dominant movement. The findings indicate some difference in cortical activity relating to dominant and non-dominant hand movement.

Adult↗
PubMed1987

Changes of electrically elicited reflexes in hand and forearm muscles in man.

Cutaneo-muscular reflexes with short and long latency excitatory phases following digital nerve stimulation were observed in the first dorsal interosseus muscle of the hand in healthy subjects. The short latency reflex was obtained also with the H-reflex method in the flexor carpi radialis muscle, stimulating the median nerve, with a mean latency (+/- SE) of 15.4 +/- 0.5 ms. The height of the subject correlated with the H-reflex latency. The amplitudes of maximal M-response and maximal H-reflex were higher in athletes than in normals. During weak voluntary contraction of the muscle studied the 50% H-reflex amplitude increased and during passive stretching of wrist flexors the resting amplitude of the 50% H-reflex decreased.

Adult↗
PubMed1986

Mechanically induced reflex responses in human triceps brachii.

The short and long latency reflex responses of human triceps brachii muscle were recorded in 14 healthy volunteers. An electromechanical hammer was used to stretch the muscle and recordings were made from a surface electromyogram. The monosynaptic tendon reflex occurred at a mean latency of 12.5 ms (SE 0.7 ms). Later responses were observed in activated conditions (weak force production, preparatory period) at a mean latency of 62.8 ms (SE 3.5 ms). The amplitude of the short latency reflex increased during weak tension, the long latency reflex amplitude seemed to increase during the preparatory period testing. The amplitude increases can be attributed to increased lower motoneuron excitability even during weak voluntary activity. The tendency towards an increased amplitude during the preparatory period may be connected with the higher regulation of the long latency reflex.

Adolescent↗
PubMed1986

Changes in the probability of firing of motor units following electrical stimulation in human limb muscles.

Changes in the probability of motor unit firing was studied in ten different muscles (six muscles in the upper extremity and four muscles in the lower extremity) of eleven healthy human subjects. The responses were elicited by the electrical stimulation of cutaneous or mixed nerves during weak voluntary contraction of the muscle studied, and were recorded by averaging the rectified surface electromyogram. In eight of the ten muscles, well-detectable, short and long latency excitatory phases were observed. The most constant and well-identified excitatory responses were observed in the first interosseus dorsalis muscle in the hand, and in the extensor digitorum brevis muscle in the foot. These two distal muscles seem to be the most useful muscles for routine determination of the short and long latency responses to cutaneous stimulation.

Adult↗
PubMed1986

Short and long latency reflex responses elicited by electrical and mechanical stimulation in human hand muscle.

The relationship between electrically and mechanically induced reflex responses in the rectified, averaged surface electromyogram of the first interosseus dorsalis muscle was examined in 18 healthy human subjects. Both methods evoked identifiable short and long latency reflex responses. The onset latencies for short latency reflexes with electrical and mechanical stimulations were 30.6 ms (+/- 2.2 ms) and 28.9 ms (+/- 2.2 ms) and for long latency reflexes 50.0 ms (+/- 2.8 ms) and 51.2 ms (+/- 5.2 ms), respectively. The correlation of the onset latencies of the reflexes revealed significant correspondence between the electrical and mechanical methods implying at least partly mutual mechanisms.

Adolescent↗
PubMed1986

Short and long latency reflexes in human muscles following electrical and mechanical stimulation.

Electromyographic (EMG) recordings were made during slight voluntary contraction or during rest in various human muscles following electrical and mechanical stimulation. The electrical stimuli used in most of these experiments were square wave pulses with the duration of 100 microseconds given at a frequency of 3 Hz on cutaneous and mixed nerves. The mechanical stimuli were constant stretches of the muscle induced by taps of the electromechanical reflex hammer. The aims of the series of studies were to investigate the characteristic features of electrically and mechanically elicited muscular responses, the correspondence between electrically and mechanically elicited responses, the short latency response following muscle afferent stimulation and the modifications of the electrically elicited responses. The electrical stimulation during slight voluntary activity caused short and long latency excitatory phases in averaged and rectified EMG with the onset latencies much shorter than the voluntary reaction time. The responses were considered reflexive. The most constant short and long latency reflexes following electrical stimulation were found in the first dorsal interosseus muscle in the hand and in the extensor digitorum brevis in the foot. The mean onset latency for the short latency reflex was 30.9 +/- 1.7 ms (SD) and for the long latency reflex 50.9 +/- 2.8 ms in the hand muscle. In the foot muscle the mean short latency reflex latency was 54.9 +/- 4.1 ms and the long latency reflex latency was 80.5 +/- 5.5 ms. The onset latencies of the short and long latency reflexes during slight voluntary activity following stretching and following cutaneous nerve stimulation corresponded in the first dorsal interosseus muscle. It was concluded that they are generated at least partly via mutual pathways. The stretches given to the triceps brachii muscle during various head positions, different elbow angles and during the Jendrassik maneuver revealed short latency reflex facititations. The lesser degree of the facilitation was caused by the tonic neck reflex and the Jendrassik maneuver caused the greater degree of the facilitation. The short latency reflex following muscle afferent stimulation (the H-reflex) was elicited in the flexor carpi radialis muscle with a mean latency of 15.4 +/- 0.5 ms. The amplitude of the 50% H-reflex was modified by contracting or by stretching of the muscle. Voluntary contraction increased the 50% H-reflex amplitude about 30% and the passive stretching decreased it to about 80% of the control value. The patients with different central nervous system disorders showed abnormal electrically elicited short and long latency reflexes. The s

Adult↗
PubMed1985

Electromyographic responses elicited by cutaneous and mixed nerve stimulation in human tibialis anterior muscle.

The rectified and averaged myoelectrical responses of the anterior tibial muscle to stimulation of the posterior tibial, peroneal and sural nerves at the ankle were recorded during a weak isometric contraction in man. The stimulation of the posterior tibial nerve elicited two excitatory phases (short and long latency excitations) at 40 ms and 78 ms latencies, respectively, separated by a phase of reduced activity. With peroneal and sural nerve stimulation such triphasic responses were less consistent; only a monophasic inhibitory response occurred in some recordings. These results indicate that well-identifiable responses with distinct latencies can be obtained in human leg muscle with cutaneous and mixed nerve stimulation distal to the muscle.

Adult↗
PubMed1985

Short latency somatosensory evoked potentials during active hand movements.

This study was designed to investigate the effect of active movement on spinal and cortical evoked responses. During voluntary hand movements the cervical and cortical short latency somatosensory evoked potentials (SEP) elicited by stimulation of the median nerve at the wrist were studied in nine healthy subjects. The latencies of the SEPs were not affected by active movements whereas the peak to peak amplitudes of the main cervical (N13-P15) and the main cortical (N20-P25) deflections were significantly reduced. The cortical subcomponents (N16 and N17), probably reflecting thalamic and thalamocortical activity, were not significantly affected by movements. The amplitude reductions in the cervical and cortical recordings might be related to proprioceptive feedback from the muscle afferents.

Adult↗
PubMed1983

Characteristics of the triceps brachii tendon reflex in man.

The quantitative characteristics of the triceps brachii tendon reflex have been investigated in nine healthy adults. Particular consideration was given to the normal latency and amplitude values in response to a standardized tendon percussion. The effects of Jendrassik maneuver, head position (tonic neck reflex influences) and elbow joint angle were also evaluated. The latency of the triceps brachii reflex (mean = 11.2 msec) under normal conditions was found to be substantially shorter than previously reported values for the monosynaptic response. These differences are apparently attributable to the different methods that have been used to elicit the reflex. The present results are shown to be quite compatible with the known conduction velocity properties of the radial nerve. The mean amplitude of the reflex (means = 1.6 mV) was shown to be significantly (p less than 0.05) influenced by head position and Jendrassik maneuver. The magnitude of these effects are interpreted with respect to the proportion of the motoneuron pool activated by Ia inputs. Their neurophysiological basis and clinical usefulness are also discussed briefly.

Adult↗
PubMedDate not supplied

The N30 component of somatosensory evoked potentials in patients with dystonia.

We recorded short-latency median nerve somatosensory evoked potentials (SEPs) in 10 patients with dystonia (6 with focal dystonia, 3 with generalized dystonia, and 1 with segmental dystonia) and compared them with those of 10 normal controls. The EEG was recorded from 29 sites on the scalp with linked earlobe electrodes for reference. Latencies and amplitudes of P15, postcentral N20 and P45, and frontal N30 were evaluated. The latencies of all potentials were the same in patients and controls. The amplitudes of P15, N20 and P45 were also the same in both groups, but the N30 amplitude of the patients was larger than of the controls. The amplitude of N30 did not vary from the affected side to the unaffected side. Previous work has shown decreased N30 amplitude in patients with Parkinson's disease. Changes in N30 amplitude may be indicative of abnormal excitatory effects on cortex resulting from disorders of the basal ganglia.

Adult↗
PubMedDate not supplied

Altered frontal lobe function suggested by source analysis of event-related potentials in impulsive violent alcoholics.

Scalp-recorded event-related potentials (ERPs) are sensitive indicators of subtle alterations in cerebral processes. We assessed automatic auditory adaptation and detection of novel stimuli in violent and non-violent alcoholics and normal subjects. Source analysis of ERPs revealed active medial temporal and frontal regions in all subjects. Frontal lobe processed alerting tones in violent alcoholics, whereas non-violent alcoholics and normal subjects processed them in medial temporal brain areas. Detection of deviant tones appeared simultaneously in frontal and temporal areas in violent alcoholics, but sequentially in other groups. These findings imply alterations in arousal and involuntary adaptive processes in cortical networks associated with violent behaviour and alcoholism.

Adult↗
PubMedDate not supplied

Long-latency stretch reflex induced by tendon jerk in human triceps brachii muscle.

The electrical activity of the human triceps brachii muscle was recorded with surface electrodes in 14 healthy volunteers. Three experimental conditions were used to analyze muscle responses produced by tendon tap with an electromechanical hammer: 1) the muscle was at rest, 2) the subjects maintained an isometric tension for constant background EMG activity and 3) the subjects were asked to extend their arm in response to an acoustic signal occurring simultaneously with the tap. The analyses were performed with a computer. The monosynaptic tendon reflex had a mean latency of 12,5 ms. Later responses were observed with a mean latency of 62.8 ms. The later response observed in the extension experiments showed a synchronous EMG activity in comparison to the voluntary activity. It seems likely that proprioceptive impulses are of major importance in producing also the late responses since the method used minimalized cutaneous and joint afferent inputs.

Adolescent↗