2a. The facts that have been discovered in regard to the localization of certain psycho-physical functions in the cortex, are derived partly from pathological and anatomical observations on men and partly from experiments on animals. They may be summed up as follows: 1) Certain cortical regions correspond to certain peripheral sensory and muscular regions. Thus, the cortex of the occipital lobe is connected with the retina, a part of the parietal lobe with the tactual surface, and a part of the temporal with the auditory organ. The central ganglia of special groups of muscles generally lie directly next to or between the sensory centres functionally related to them. 2) Certain complex disturbances have been demonstrated when certain cortical regions which are not directly connected with peripheral organs, but are inserted between other central regions, fail to carry out their functions. The only relation of this kind which has been proved with certainty, is that of a certain region of the temporal lobe to the functions of speech. The front part of this region is connected in particular with the articulation of words (its disturbance results in interference with motor coordination, so-called "ataxic aphasic"), the part further back is connected with the formation of word-ideas (its disturbance hinders sensorial coordination and produces in this way the so-called "amnesic aphasia"). It is also observed that these functions are as a rule confined entirely to the left temporal lobe and that generally apoplectic disturbances in the right lobe do not interfere with speech, while those in the left lobe do. Furthermore, in all these cases, in both simple and complex disturbances, there [p. 206] is usually a gradual restoration of the functions in the course of time. This is probably effected by the vicarious functioning of some, generally a neighboring cortical region in place of that which is disturbed (in disturbances of speech, perhaps it is the opposite, before untrained, side that comes into play). Localization of other complex psychical functions, such as processes of memory and association, has not yet been demonstrated with certainty. The name "psychical centres", applied to certain cortical regions by many anatomists, is for the present at least based exclusively either on the very questionable interpretation of experiments on animals, or else on the mere anatomical fact that no motor or sensory fibres running directly to these regions can be found, and that their connective fibres in general are developed relatively late.
The cortex of the frontal brain is such a region. In the human brain it is noticeable for its large development. It has been observed in many cases that disturbances of this part of the brain soon result in marked inability to concentrate the attention or in other intellectual defects which are possibly reduceable to this; and from these observations the hypothesis has been made that this region is to be regarded as the seat of the function of apperception which will be discussed later (4), and of all those components of psychical experience in which as in the feelings, the unitary interconnection of mental life finds its expression (comp. p. 89). This hypothesis requires, however, a firmer empirical foundation than it has at present. It is to be noted that those cases where, in contrast with the first ones, mentioned, a partial injury of the frontal lobe is sustained without any noticeable disturbance of intelligence, are by no means proofs against this hypothesis. There is much evidence to show that just here, in the higher centres, local injuries may occur without any apparent results.
This is probably due to the great complexity of the connections and to the various ways in which the different elements can, therefore, take the place of one another. The expression "centre" in all these cases is, of course, employed in the sense that is justified by the general relation of psychical to physical functions, that is, in the sense of a parallelism between the two classes of elementary processes, the one regarded from the point of view of the natural sciences, the other from that of psychology (comp. § 1, 2 and § 22, 9). [p. 207]
3. The interconnection of psychical processes, which constitutes what we understand under the concept consciousness, is in part a simultaneous, in part a successive interconnection. The sum of all the processes present at a given moment is always a unitary whole whose parts are more or less closely united. This is the simultaneous interconnection.
A present state is derived directly from that immediately preceding either through the disappearance of certain processes while others change their course and still others begin, or, when a state of unconsciousness intervenes, the new processes are brought into relation with those that were present before. These are successive interconnections. In all these cases the scope of the single combinations between preceding and following processes determines the state of consciousness. Consciousness gives place to unconsciousness when this interconnection is completely interrupted, and it is more incomplete the looser the connection of the processes of the moment with those preceding, Thus, after a period of unconsciousness the normal state of consciousness is generally only slowly recovered through a gradual reestablishment of relations with earlier experiences.