1450 



MAMJI'.i II >K 111- 1*1 IS SH il I n.s 



NEUROPHYSIOLOGY III 



deduced bs Haller in 1765; Bell and Miiller agreed 

 with this opinion. Morn in [825 showed experi- 

 mental]) that different regions of the tongue were 

 mure or less sensitise to various taste stimulating 

 substances. Tin- taste buds were identified and de- 

 scribed by both Schsvalbe and Losen in 1807. But 

 c\<n after the specific nerve energy theory had 

 been formally proclaimed, and thus the importance 

 of isolating specific receptor- emphasized, no evi- 

 dence was forthcoming which would make possible 

 the identification of structural differences among the 

 receptors, differences which might be correlated with 

 differences in function. Numerous investigators ex- 

 plored the tongue of human subjects, recorded 

 the ta-te sensations reported in response to stimula- 

 tion with different substances and prepared schemes 

 for classifying the sensory qualities of taste. 



The olfactory receptive area was described in 

 1882 by Schultzc but, as with the taste buds, no 

 evidence was obtained which suggested a relation 

 between types of receptor and olfactory sensations. 

 Man) elaborate schemes of classifying discriminable 

 odors were constructed on the basis of psychophysical 

 experiments. 



( 1 1, nlcs Bell is sometimes given credit for dis- 

 covering the muscle sense, bul historians have pointed 

 out that a number of other investigators had pub- 

 lished papers suggesting a sixth sense before Bell's 

 1 8^6 publication. They had been less successful in 

 getting the idea of an additional sense adopted. 

 Sensors receptors (muscle spindles) in muscle were 

 firsl isolated b) ECuhne in 1863. Sherrington in 1894 

 showed that the muscle spindles wen- innervated b) 

 nerve libers from the dorsal spinal roots and pre- 

 sumabl) had .1 sensor) function. 



Although the vestibular sense was not at the time 

 considered to belong with the other prim. us senses, 



the presence ol sense organs in the nonauditory laby- 

 rinth which were stimulated by position or movement 



ol the he. id had been de iMi.iieil bv f'liiorcns in 



i"..'l Sim, stimulation ol the vestibular end organ 

 due- not give rise 10 specific, qualitatively distinct 

 sensations in the same way that stimulation <>l other 



sensors organs does, ni> attempt was nude in classif) 



qualities of vestibular sensation. Nevertheless, Fluorens 

 .md later investigators did seek in discover separate 

 linn linns ini the major subdivisions of the vestibular 

 end ni',;. in, name!) the semicircular canals, the 

 mi tde .md the " < m!i 



I oincident with the development ol these new 

 hypotheses .is in die anatomical and physiological 

 bases ui sensor) discrimination was another line oi 



attack upon the problem of how the physical world is 

 perceived by the living organism. E. 11. Weber in 

 1834 began, and G. T. Fechncr during the period 

 1 85 1 -1 879 and W. Wundt from 1858 to 1920 ex- 

 tended a series of experimental investigations in 

 which the aim was to establish systematic relation- 

 ships between the physical attributes of external 

 stimuli and the psychological attributes of sensation. 

 Their svork in this new field, later labeled psycho- 

 physics, established the foundation upon which was 

 built a new branch of science, experimental psychol- 

 ogy. Although the procedures which they and their 

 followers used did not call for direct observation of 

 physiological events, the theories of sensation to 

 which the psychophysicists contributed have usually 

 been expressed in terms of physiological events. In 

 many instances, the results of psychophysical studies 

 base set problems for physiological investigations. 

 Psychophysics has also made important contributions 

 to physiology of sensation by its desclopment of 

 methods of measurement, particularly methods of 

 measuring absolute and differential thresholds, and 

 by creating and assisting in satisfying a need for 

 instruments which make possible the production 

 and exact control of physical stimuli. 



The last half of the nineteenth century was marked 

 by a number of other developments which were 

 important to the advance in scientific knowledge 

 of sensory discrimination. Increased interest in the 

 sense organs and the central nervous system led to 

 their careful examination by microscopic techniques. 

 The techniques, at first crude the dissection and 

 examination of fresh tissues under the microscope — 

 were rapidl) improved. Sense organs and neural 



tissues were treated with fixatives or hardening 

 solutions, thus making dissection easier. A next and 

 more important step forward was taken when analy- 

 tical staining methods were discovered lis Golgi 

 in 1873 and Ehrlich in 1886. Their methods and 

 tlio-e developed b) others such as Ramon \ Cajal, 

 Nissl, Weigert and Marchi began to reveal for the 

 Inst time details of the structures w hich mediate 



sensation. 



The neural pathways were traced from sense or- 

 gans into the central nervous system and, at least 

 parti) because of the influence of specific nerve en- 

 erg) theory, localization of separate regions sub- 

 seising iln different senses was sought in the highest 

 centers, particular!) in the cerebral cortex. 1 In- 



methods of architectonics were applied, and the 



cortex was subdivided into man) regions of sup- 

 posedl) special function, the sensor) projection 



