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Biomedical subjects

U Tan

Publications and source records attributed to U Tan.

At least 109 records · Page 6Linked to original sources
PubMed1987

Paw preferences in dogs.

The distribution of paw preferences were studied in 28 dogs. The paw preference was assessed by counting the right and left paw movements performed to remove an adhesive plaster from the eyes. The significance of the right minus left paw reaches in percentages was evaluated statistically in each animal. There were three distinct groups in respect to paw preferences in dogs: right-preferent (57.1%), left-preferent (17.9%), and ambidextrous (25.0%). Statistical analysis showed that the observed frequencies for each group were not merely chance variations which would be expected in a random sample. It was concluded that the population bias can be expressed in a distribution skewed toward a right-hand bias as seen in man.

Animals↗
PubMed1987

Asymmetries in the cerebral dimensions and fissures of the dog.

The surface dimensions and fissures of the right and left cerebral hemispheres were compared in dogs. The right hemisphere was significantly larger in length and height than the left hemisphere; there was no significant difference in the width of the right and left hemispheres. The mean length of the cruciate sulcus did not significantly differ on the right and left sides except individual for asymmetries. The difference in the mean length of the right and left Sylvian fissures was not significant, but the right Sylvian fissure was significantly lower than the left. The base of the right planum temporale tended to be larger than the left. These anatomical asymmetries did not correlate with paw preference. The data are consistent with notion that asymmetrical patterns cannot be a distinctive feature of the human brain.

Animals↗
PubMed1986

Symmetric distribution in latencies of cortical somatosensory potentials evoked by right and left posterior tibial nerve stimulation in right-, left-, and mixed-handed men and women.

The latencies of the P1, N1, P2, and N2 components of the somatosensory potentials evoked by stimulation of the right and left posterior tibial nerves in the right-, left-, and mixed-handed men and women were subjected to a statistical analysis. The mean latencies of the primary and secondary cortical responses are symmetrically distributed between the right and left sides for all the subjects. The mean latencies obtained of women were significantly shorter than those of men. This difference was accounted for by the fact that the mean body height of women was significantly less than that of men, since there was a significant positive correlation between body height and latency. It was concluded that the conduction times for the cortical input as well as the early cortical information processing, despite synaptic interventions, cannot play a role in the cerebral lateralization concerning the perceptual and manipulospatial tasks.

Adult↗
PubMed1986

Modulation of spinal motor asymmetry by neuroleptic medication of schizophrenia patients.

The effects of chlorpromazine treatment on spinal motor asymmetry was studied in right-handed chronic schizophrenia patients. Spinal motor asymmetry and lower motor neuron excitability were tested by the Hoffmann reflex recovery curve. In drug-free patients, the Hoffmann reflex recovery curve from the left leg was significantly higher than that from the right leg as in the healthy subjects. This spinal motor asymmetry disappeared and even reversed within three weeks of the neuroleptic treatment. The chlorpromazine medication lowered the left recovery curve predominantly, and slightly augmented the right recovery curve. These results do not support the hypothesis that schizophrenia may be related to an overactive, and yet functionally deficient, dominant hemisphere. It was concluded that the cooperative function of both cerebral hemispheres should be taken into consideration to explain the neural mechanisms of schizophrenia.

Adult↗
PubMed1985

Left-right differences in the Hoffmann reflex recovery curve associated with handedness in normal subjects.

The relation between handedness and the Hoffmann (H) reflex recovery curve was studied in normal subjects. In right handers, the H response recovery curve from the right leg was significantly lower than that from the left leg. The opposite finding was obtained from the left handers. In mixed handers (ambidexters), there was no significant difference between the recovery curves from the right and left legs. It was concluded that there is a close relationship between handedness and the height of the H response recovery curves from the right and left sides.

Female↗
PubMed1985

Velocities of motor and sensory nerve conduction are the same for right and left arms in right- and left-handed normal subjects.

The velocities of motor and sensory conduction of median and ulnar nerves were measured on the left and right arms of 33 right-handed and 12 left-handed normal subjects. Contrary to current knowledge there was no statistically significant difference in the velocities of nerve conduction on the left and right sides of these subjects. It was suggested that the differences in the velocities of nerve conduction cannot contribute to the mechanisms of handedness.

Adult↗
PubMed1985

Entropy concept in relation to brain waves and evoked potentials: critique of a physical approach.

Basar's view that the larger the number of synchronized and coupled participating neural generators, i.e., the lower the entropy of the neural systems, the lower the responsiveness of the system, and vice versa, was reconsidered experimentally and theoretically, in the light of current knowledge about the relationship between EEG states and evoked potentials. It was found that the morphology as well as the magnitude of the somatosensory evoked potentials was the same during synchronized (low entropy) and desynchronized (high entropy) EEG states in normal human subjects. Baclofen caused an increase in the somatosensory evoked potentials without affecting the EEG in unanaesthetized dogs. In the less complicated and more limited systems such as the skeletal muscle and monosynaptic reflex paradigms, an inverse relationship was established between the entropy state and responsiveness. This relationship can be simply explained by the neurophysiological facts such as Na-inactivation process at the excitable membranes and the refractory states of the neural generators. These results are consistent with those from the literature; the evoked potentials are usually large when recorded during synchronized EEG states and vice versa. It is suggested that, at least, the well established neurophysiological facts should not be ignored in physical approaches to neural mechanisms, especially when it concerns highly complex systems such as the brain.

Animals↗
PubMed1985

Relationships between hand skill and the excitability of motoneurons innervating the postural soleus muscle in human subjects.

The relation of hand skill to the excitability of motoneurons innervating the postural soleus muscle was studied in normal human subjects. The motoneuronal excitability was tested by the recovery curve of the Hoffmann reflex. The hand skill was assessed by the peg moving test. Females have been found to be better than males in hand skill. It was established that the H response recovery curve from the right leg was significantly lower than that from the left leg in right handed subjects. The opposite was found in left handers. In ambidexters, there was no significant difference between the heights of the left and right recovery curves. The laterality quotients of the H response recovery curves were normally distributed in the total sample with a mean significantly less than zero, indicating a left shift bais in the motoneuronal excitability. The possible factors contributing to the inverse relationship between hand skill and the excitability of motoneurons innervating the postural soleus muscle were discussed in light of genetic determinants of brainedness and the corticospinal inputs to postural motoneurons.

Adult↗
PubMed1984

Lateral asymmetry of H-reflex recovery curves in cat: evidence for a spinal motor asymmetry.

Recovery curve of the Hoffmann reflex from the left and right sides was studied in lightly anesthetized cats before and after spinalization. According to the differences in the H-reflex recovery curves from the left and right lateral gastrocnemiussoleus nerves, three populations of intact animals were found: right dominant with higher recovery curve on the right side (31.8%), left dominant with higher recovery curve on the left side (36.4%), and ambilateral with no dominance (31.8%). After spinalization the dominance remained the same in the two first groups and dominance appeared in 5 out of the 7 cats of the last group. These results provide evidence for a bilateral asymmetry of alpha motoneuron excitability in cats, which can be used as a model to study the possible mechanisms of spinal motor asymmetry.

Animals↗
PubMed1983

Excitatory and inhibitory effects of repetitive stimulation of group I and II extensor afferents on homonymous motoneurons.

The repetitive firing of functionally isolated 143 extensor alpha motoneurons in response to homonymous group I and II tetanizations was studied in decerebrate cats. Of a total sample of 92 group I activated motoneuronal units, 76 motoneurons (82.6%) discharged phasically and 16 motoneurons (17.4%) discharged tonically at threshold or just suprathreshold tetanizations. Only 6 of the phasic motoneurons fired tonically when the stimulus strength was increased within the group I range. The firing rate of 8 phasic motoneurons increased at group I and II stimulations, but they retained their phasic discharge characteristics. The remaining 46 group I activated phasic motoneurons (60.1%) delivered tonic discharges when group II afferents were stimulated. Another group of 16 phasic motoneurons (21.1%) became tonic at group II tetanus, but their tonic discharge was usually interrupted by an inhibitory period, which coincided with an escape reaction of the animal. Out of 38 group II activated motoneuronal units, only 8 (21.1%) motoneurons discharged tonically at threshold or just suprathreshold tetanizations. The repetitive activity of these motoneurons was usually interrupted by an inhibitory period, which coincided with an escape reaction of the animal. This inhibition disappeared after procain application to the GS nerve, and was attributed to dominant inhibitory action of group II afferents mediating the sensation of pain. The remaining 30 (78,9%) motoneurons discharged phasically. Six of them remained phasic even at high threshold group II tetanus. The others gave tonic discharges when the stimulus strength was increased within the group II range. A great percentage of motoneurons discharged regularly with a fixed decoding ratio reflecting monosynaptic excitation. Some motoneurons discharged in multiple bands of impulse intervals due to a variable decoding ratio, which can be attributed to both monosynaptic and polysynaptic reflex discharge elicited by group I and/or II tetanizations. There were 6 motoneurons (4.2%), which discharged repetitively at stimulations of the GS, DP, and SUR nervers. These motoneurons were referred to "common motoneurons", which may participate in multiple motor actions such as fixation of a limb or as a part of the flexor reflex. SOL motoneurons usually discharged tonically at tetanizations within the group I range. The firing rate of these motoneurons usually decreased at tetanizations of the group II afferents of MG nerve. Conversely, tetanization of the group II afferents of SOL nerve usually exerted facilitatory effects on group II activated MG motoneurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1978

Electrocorticographic effects of topically applied scopolamine.

The electrocorticographic effects of topically applied scopolamine were investigated in unanesthetized cats with high cervical transection. After subpial injection of 30 cumu scopolamine in concentrations of 10 to 20%, large amplitude intermittent sharp waves appeared in the electrocorticogram, which developed into long-lasting paroxysmal activity. This effect was antagonized by intravenous eserine, 0.1 mg/kg, when it was produced by topical scopolamine in low dosage. The acoustically evoked cortical response and the generalized epileptiform activity produced by topical succinylcholine disappeared after topical scopolamine in low dosage. It is suggested that the seizure-suppressing effect of scopolamine may be due to its cholinolytic action. The convulsive activity of topical scopolamine in high concentrations may be accounted for by its depolarizing, synchronizing, disinhibiting, and acetylcholine-releasing effects.

Administration, Topical↗