Bilateral Matching Research Articles

Superposition of H reflexes on steady contractions in man.

1. The aim of the investigation was to study the influence of steady isometric contractions on H reflexes of human soleus muscle. 2. Stimulating and recording conditions were hardly affected by plantar flexions which subjects maintained in a force matching task. 3. If the interval between a preceding control and the test stimulus was less than 8 s the test H reflex was depressed in the relaxed subject. The depression was diminished or removed if the test reflex was superimposed on a background activity. The interval between control and test H reflex was at least 8 s in the following experiments. 4. H reflexes were nearly independent of steady plantar flexions on which they were superimposed. In some subjects, there was a slight increase with increasing torque. During dorsal flexions, H reflexes in all subjects were inhibited with increasing torque. 5. The relationship between test H reflexes, control H reflexes and background activity was evaluated by varying pseudo-randomly stimulus intensity and steady flexion torque. The surface defined by this three-dimensional relation approximated a plane suggesting linear properties of the H reflex. In some subjects threshold intensity decreased slightly with torque, in others it was constant. 6. In response to a warning signal, human subjects initiated steady plantar or dorsal flexions in both feet and, at the same time, they started to concentrate on a light at the onset of which they performed a unilateral ballistic plantar contraction as fast as possible. The relations between H reflex and maintained flexion force during the warning period of the reaction time task were identical to those during force matching, showing that the behavioural context did not modulate the relations. 7. The relations were also the same if reflexes were evoked bi- or unilaterally, illustrating the absence of a mutual modification of simultaneously evoked H reflexes. 8. The relation was the same with ipsilateral matching and relaxed contralateral muscles as with bilateral matching. If the ipsilateral side stayed flaccid contralateral matching increased H reflexes by about 20% above control values. 9. It was concluded that various factors can combine to produce an increase of H reflexes with torque, the most important of them being the use of short intervals between H reflexes. We have various evidence from the present experiments for believing that, in the relaxed subjects, the subliminal fringe was small and that although stimulus intensities below threshold could evoke an afferent volley, the effect of this on low-threshold motor units was prevented by presynaptic inhibition at the Ia terminals.

Electroencephalographic studies in “split brain” cats

1. 1. The EEG activities of homologous cortical areas of the cat brain have been recorded in chronic conditions. When the EEG displays slow wave-spindle patterns, the potentials simultaneously recorded from corresponding points of the two hemispheres are essentially similar. 2. 2. The normal EEG bilateral symmetry is disrupted permanently by section of corpus callosum. In the callosotomized animal, however, EEG arousal reactions and onsets of sleep patterns remain synchronous in the two sides. Similar EEG features have been found in a cat with anomalous absence of corpus callosum. 3. 3. When division of all the other forebrain commissures and midsagittal section of the rostral midbrain are added to that of the callosum, a mismatching of the EEG waking and sleeping states in the two hemispheres can be observed for a maximum period of 8–10 days. It has been attributed to asymmetrical parasagittal lesions in the region of the rostral midbrain. Recovery of the normal bilateral matching is always complete. 4. 4. It is concluded that while the corpus callosum is essential for the maintenance of the fine bilateral correspondence of the EEG waves, the sleep-wakefulness cycle in the two separated hemispheres is controlled by the lower brain-stem.