Outlines of physiological psychology : A text-book of mental science for academies and colleges.

  • Ladd, George Trumbull.
Date:
1893
Catalogue details

Licence: Public Domain Mark

Credit: Outlines of physiological psychology : A text-book of mental science for academies and colleges. Source: Wellcome Collection.

Provider: This material has been provided by The University of Leeds Library. The original may be consulted at The University of Leeds Library.

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    the strength of the stimulus. Or if the gray surface be wholly removed, and the stimulus applied to the blood in the cavity, the customary result follows. From these and other facts it has been argued that these areas are not true cortical motor centres. In answer to objections like the foregoing the following, among other similar arguments, are urged. When the animal is deeply etherized, the excitability of the cortical regions is wholly or partly lost. This could scarcely hap- pen if the substance of these regions acted only as a homo- geneous conducting medium for the electrical current. It is also found by most observers that a stronger stimulus is necessary to move the muscles from these centres, after the gray substance of the surface has been removed. The electrical current seenis also to be retarded in passing through this superficial matter; it is a fair assumption, then, that the interval is spent in evolving the particular nervous function which belongs to this matter. Indeed, that the evidence from stimulation connects certain por- tions of the gray surface of the brain with the movements of certain groups of muscles, in a peculiar way, is now scarcely to be denied by any one acquainted with the nature and extent of the phenomena. Evidence from Extirpation. — It is natural to argue that those areas of the cerebral cortex, whose loss is followed by the loss or disturbance of motion in definite groups of mus- cles, or by the loss or disturbance of any class of sensory impressions, are functionally related in some peculiar way to such muscles or organs of sense. The argument, how- ever, needs caution in application. For in the first place, it is impossible at each stage of the experiment to know what is the precise condition of the brain. Local and extensive inflammations, secondary lesions and degenerations of the nerve-tracts, cannot easily be followed by the experimenter in detail. It is generally found that the effects of extir-