1464 



llWIIBIlllK OF I'lIVSIOI.OCV 



NEUROPHYSIOLOGY III 



was carefull) measured before and after experimental 

 ablations of neural structures. As mentioned above, 

 disturbances in placing and hopping reactions occur 

 parietal lobe ablations; spatial cues are to some 

 extent involved in these responses. 



In clinical eases, loss of ability to recognize position 

 of limbs and movements of the limbs in space has I ieen 

 Stressed by I lead & Holmes and others as a prominent 

 symptom of damage to the somesthetic cortex. 



pattern discrimination. Except under the carefully 

 controlled conditions of the laboratory, most sensory 

 discriminations made by man or other higher animals 

 are discriminations of changes in temporal and spatial 

 patterns of physical events. Techniques have not 

 yet been devised so that we can get a good picture 

 of the complex neural activity aroused by patterns 

 of end-organ excitation. However, in behavioral 

 studies aimed at clarifying the role of higher centers 

 til the central nervous system in sensory discrimina- 

 tion, patterns of sensory stimuli have often been used, 

 both in experimental and clinical investigations. 



In all animals that have been studied (rat, cat, dog, 

 monkey and man), it has been found that capacity' to 

 iIim riminate visual patterns is permanently lost after 

 bilateral total ablation of the visual cortex. Small 

 remnants of the visual projection areas are sufficient 

 to mediate discriminations of simple patterns. In the 

 rat, Lashley (119) has estimated that pattern dis- 

 crimination is not destroyed if an amount of cortex 

 equal to about one sixtieth of the total is spared in 

 the macular projection region. Deficiencies in visual 

 pattern discrimination have been reported in some 

 studies after ablation of preoccipital cortex (1, 2) and 

 of association cortex in the parieiotemporopreoccipi- 

 t.il region (38). 



Discrimination of tonal patterns has been studied 

 b) Diamond tV Nell (52) in the eat and bv Jcrison & 

 Nell (104) in the monkey. The sound patterns used 

 in these experiments were temporal rather than 

 spatial, i.e. thev consisted of a change in the temporal 

 sequence of pulsing tones. In the cat, complete bi- 

 lateral ablation oi the auditor) projection areas I, II 

 and Ep (areas defined bv evoked potential mapping) 



led to I11t.1l loss <>l capacitv for pattern discrimination. 



\ m. ill remnant oi auditor) cortex permitted re- 

 let 11" oi the pattei n disi rimination habit I hat the 



loss after total ablation was .1 loss ol capacit) to 

 rei ognize the patterning of the physical stimulus was 

 mown bv control tests which revealed thai the same 

 animals which could nol do pattern discrimination 

 could discriminate changes in frequency. Goldberg 



el al. (76) have also reported that ability to discrimi- 

 nate temporal patterns of tones is affected in the cat 

 after bilateral ablation of insular-temporal cortex 

 ventral to the region defined as auditory cortex by 

 evoked potential mapping. 



Considered only casually, the striking parallel be- 

 tween the visual and auditor) systems with respect to 

 cortical function in pattern discrimination may not 

 at first be apparent. In the case of the v isual system, 

 we speak of a loss of capacity to discriminate spatial 

 patterns; for the auditory system, a loss of capacity to 

 discriminate temporal patterns. But, when we look 

 more closely at the order of events in the central 

 nervous system, it becomes clear that the spatial 

 patterns at the retina and the temporal patterns at the 

 basilar membrane become, in the peripheral nerve 

 and in higher centers, patterns of nerve impulses 

 which differ both in space and in time. 



It is probably impossible to stimulate the retina in 

 such a fashion that a pattern of nerve impulses is set 

 off having only space, or place, differences. As 

 Lashley has pointed out (120), even with tachisto- 

 scopic presentation of light stimulus, the aftereffects 

 will likely produce a train of nerve impulses. Further- 

 more, if the activity in the first or second order neurons 

 had only spatial patterning, it must inevitably have 

 temporal patterning as well bv the time it arrives at 

 higher centers because of such factors as differences 

 in conduction rale and dillerences in number of 

 synapses crossed. 



Similarly, temporal patterns of tones presented to 

 the cochlea elicit not onlv a temporal sequence of 

 events in the peripheral nerve but, at least when more 

 than one tonal frequenc) is used, there will be spatial 

 dillerences as well. 



Capacitv to discriminate tactual patterns has also 

 been measured before and after cortical ablations. 

 The experiments have been less adequate than those 

 for vision and hearinu, both from the standpoint of 

 stimulus control and evaluation 11! the locus and 

 extent of the expei inientallv placed lesions. Neverthe- 

 less, the results tend to support the evidence from 

 visual and auditor) experiments that the cortical 

 projection aie.i pl.iv .1 critical role in discriminations 

 of spatial and temporal patterns. Rats and eats show 

 deficits in ability to discriminate differences in rough- 

 ness a I let lesions ol somatic areas I and II I J ;j, 2 



Monkeys are less able to discriminate forms such as 

 pyramid versus cone by tactual cues (|-j In man, 

 likewise, discriminations <>l temporal and spatial 

 patterns are severel) affected bv lesions of the parietal 



cortex I |l>, (JO, <>t' 



