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STUDIES IN THE REFLEXES OF THE GUINEA‐PIG. V.: SOME EXPERIMENTS ON THE INFLUENCE EXERCISED BY THE HIGHER CENTRES UPON THE SCRATCH‐REFLEX
Author(s) -
Brown T. Graham
Publication year - 1910
Publication title -
quarterly journal of experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0370-2901
DOI - 10.1113/expphysiol.1910.sp000076
Subject(s) - reflex , scratch , psychology , medicine , anatomy , neuroscience , materials science , composite material
1. Removal of the cortex of one cerebral hemisphere depresses the excitability of the scratch‐reflex of the Brown‐Séquard phenomenon upon the contralateral side, or abolishes it completely. Where not completely abolished, the rhythm is slowed and the tonic flexion factor in the movement—as measured by the extent of the initial rise of the curve—is reduced. The extent of the clonic beats may also be diminished. In some cases this is more marked than the reduction of the tonic flexion, and in other cases the reverse is the case. 2. The effect of the removal upon the excitability of the reaction of the ipsilateral side is not one of depression. Although in some cases there may be little change, in others the excitability is increased and the rhythm of the response is quickened. A previously “incomplete” reaction may become “complete.” 3. Section of both crura cerebri in the normal guinea‐pig allows scratching movements, which may be mistaken for the movements of the scratch‐reflex, to be evoked on the application of mechanical stimulation to the skin of the neck and face. These movements are very irregular in rhythm; their rhythm is much slower than that of the scratch‐reflex; their extent is much greater; and the “tonic” factor is usually much smaller or entirely absent. These characteristics serve to distinguish the movements from those of the scratch‐reflex on careful examination. 4. Similar movements, but at first of greater regularity, are evoked after a transsection at the upper border of the pons Varolii. 5. The movements of the true scratch‐reflex persist after section of both crura cerebri. The rhythm is markedly slowed, but the extent of the beats remains the same or may be increased. The “complete reaction” of the Brown‐Séquard phenomenon may be present, but the passage of the scratching movements themselves to the opposite side has not been observed. 6. After section at the level of the upper border of the pons Varolii the scratching movements of the Brown‐Séquard phenomenon also persist, but the “complete reaction” has not been observed. The extent of the beats is increased, but the rhythm is not further altered. The “tonic” flexion factor, as measured by the rise of the curve, is decreased.