702 



SENSORY CORTICAL CENTRES. 



so. Goltz caused his servant to dress himself in a mummer's red coloured garb, which 

 preyiously had greatly excited the dog, but after the operation the dog, although it was not 

 Mind, was no longer excited thereby. Nor was it afterwards cowed by the appearance of a 

 whip. After a time there was recovery to a certain extent if the animal was trained, whether 

 by the deposition of new impressions, or by opening up new channels, or by the partial 

 recovery of some parts of the grey matter not removed, it is impossible to say.] 



[Munk has mapped out the surface of the brain into a series of 'sensory" or psycho-sensorial 

 centres, but he distinguishes between complete and total extirpation of these centres and the 

 phenomena which follow these operations.] 



When these centres are partially disorganised, the mechanism of the sensory 

 activity may remain intact, but "the conscious link is wanting." A dog with its 

 centres thus destroyed, sees, hears, or smells, but it no longer knows what it sees, 

 hears, or smells. These centres are in a certain sense the seat of experience that 

 has been acquired through the organs of sense. Stimulation of these centres 

 may give rise to movements, such as occur when sudden intense sensory impressions 

 are produced. These movements, therefore, are to be regarded as reflex, partly as 

 extensive co-ordinated reflex movements, and are in no way to be confounded with 

 the movements which result from direct stimulation of the motor cortical centres. 

 To this belongs dilatation of the pupil and the fissure of the eyelids, as well as 

 lateral movements of the eyeball. 



1. The * visual area," according to Munk, embraces the outer convex part of 

 the occipital lobe of the dog's brain. [This area and its connections are represented 

 in tig. 487. It is, therefore, in the area supplied by 

 the posterior cerebral artery.] If the occipital lobes be 

 completely destroyed, the dog remains permanently 

 blind ("cortical or absolute blindness"). If, how- 

 ever, only the central circular area be destroyed, there 

 is loss of the conscious visual sensation, which may be 

 called " psychical blindness " (Munk) [a condition of 

 visual defect like that observed by Goltz in the dog, in 

 which the dog saw an object, e.g., its food, but failed 

 to recognise it as such. There is a certain amount of 

 recovery if the whole visual area be not removed. 

 According to Schafer, the visual area of the cerebral 

 cortex in the monkey comprises the whole of the oc- 

 cipital lobe, and perhaps a part of the angular gyrus. 

 He finds, with Munk, that removal of one occipital 

 lobe is followed by hemianopia, i.e., blindness in the 

 lateral half of each retina corresponding to the side 

 operated on. The blindness passes off. Removal of 

 both occipital lobes is said to produce total and per- 

 manent blindness, whereas destruction of the cortex of 

 both angular gyri is not followed by any appreciable 

 permanent defect of vision. Ferrier, however, does not 

 accept these statements.] 

 [Ferrier and Yeo find that after operations conducted antiseptically, removal of 

 both occipital lobes (monkeys) does not cause any recognisable disturbance of 

 vision, or other bodily or mental derangement, provided the lesion does not extend 

 beyond the parieto-occipital fissure. Nor does destruction of both angular gyri 

 cause permanent loss of vision ; such loss of vision lasts only three days, so that in 

 Ferrier's original experiments, the animals lived for too short a time after the 

 operation, to enable a just conclusion to be arrived at. Destruction of both 

 angular gyri and occipital lobes causes total and permanent blindness in both eyes 

 in monkeys, without any impairment of the other senses or motor power. This 

 region Ferrier calls the " occipito-angular region." 



Fig. 487. 



Course of the psycho-optic 



fibres (after Munk). 



