Dr. Wigan's theory is inconsistent with the acknowledged fact of the existence of an im perfect symmetry of the convolutions in per sons possessing the highest order of mind. If the two brains always act in harmony, there ought to be perfect symmetry. But if we ad mit that the mind may have the initiative, then it is easy to understand how one brain may be used more than another.
That a power exists of using one brain more than another, seems probable from the more frequent and more perfect use of one hand ; and the existence of such a power implies also a capability of keeping one brain in suspense while the other is acting, under particular cir cumstances, just as we can suspend the use of one arm or one finger or one eye, although the exercise of its fellow prompts greatly to its simultaneous action.
Sleep is an affection of the centre of intel lectual action, a condition rendered necessary by the incessant working of the mind. It is indicated by the cessation of all mental nervous actions. In deep sleep the body is given up to the physical nervous actions only, without vvhich the functions of breathing, circulation, &c., could not be carried on. Dreaming occurs only in imperfect sleep,—often, if not always, just before waking,—and serves to shovv how the organic changes of the centre of intellectual action, when uncontrolled, may produce the most rapid trains of thought, recalling events or impressions that have passed away, and which we may have thoug,ht had been forgotten.
Coma is sleep of the profoundest kind, a paralysis, indeed, of the centre of intellectual action, as well as of sensation and volition. It occurs under states of disease, which induce compression of the brain, or under states of shock, vvhich suspend or greatly ditninish its natural changes, as in concussion. Or it May be induced by the influence of certain poisons of the sedative or narcotic kind, as opium and belladonna, vvhich, if given in too large a dose, paralyse first the centres of mental nervous ac tions, and ultimately those of physical nervous actions.
Somnambulism must be regarded as a state of intense dreaming, in which the person is prompted to the performance of certain acts. Talking in one's sleep, the curious changes of position which are made under the influence of nightmare, and even the most complex actions, as walking, or takino- things from one place to another or holding ;long conversation, are all induced by the same state, a morbid condition of the centre of intellectual action, generally produced by deranged assimilation or great pre vious disturbance of mind. The somnambulist, in short, is one who dreams and acts in his dream as if he were awake and as if all the phenomena of which he takes cognizance were real.
Delirium is a condition very analogrous to dreaming. The org,anic changes in the centre of intellectual action are too rapid to be con trolled by the will, or the influence of the centre of volition is impaired. The ravings of
a delirious patient generally ta.ke place uncon sciously, as if the centre of sensation were im paired likewise. In most instances, however, the patient may be roused ; a strong stimulus, as in addressing him with a loud voice, will affect his centre of sensation, and he either controls his thoughts for a brief space, and directs his attention to what is going on, or the effect of the stimulus is to direct his mvings into some new channel. The incoherent and unconnected manner in which thought follows thought in the delirious state is sufficient proof that the centre of intellectual action requires the controlling power of a will for perfect trains of thought, as much as any particular set of muscles requires the same influence for the accomplishment of definite action.
Delirium, indeed, may be viewed as a sub jective phenomenon of the centre of intellectual action, just as tinnitus aurium or ocular spectra are subjective phenomena of the centre of sen sation.
In analysing the fibres of the centrum ovale we find that a large number of them is com missural, but that the greates proportion of them serves to establish a communication be tvveen the centre of intellectual action, and the centres of volition and sensation. It is through this connection that the intellect and the will are capable of mutually affecting each other, the intellect plompting or exciting the will ; and the will, on the other hand, controlling or applying the powers of the intellect. The faculty of attention, and, therefore, in a certain degree, that of memory, are dependent on the influence of the centre of volition upon the centre of intellectual action. Every one is sen sible of a power which he possesses of fixing his attention on any given subject, as distinct as that by which he can contract any particular muscle. The association of the intellectual centre with that of sensation is necessary to en sure the full perception of sensitive impressions. The experience of each individual can supply him with numberkss instances in which, while the mind was employed upon some other oh ject of interest, an irnpression was made upon some one of the organs of sense, and indistinctly felt, but not fully perceived. When the mind has become disengaged, the fact that an impres sion had been made is recalled, without any ability to recollect its precise nature. And in many lunatics the centre of intellectual action is so irnpaired as to destroy or greatly reduce the power of perception, whilst there is abun dant evidence to shew that the affections of the organs of sense make a sufficient impression on the centre of sensation, although in such cases this centre may likewise participate in the general hebetude.