838 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



FIG. I. Weil-stained section through medulla of cat surviving 

 right hemidccortication for i month. Intact hbers between 

 degenerated right pyramid and inferior olive constitute the 

 medial lemniscus. 



count, they have recently been re-emphasized by 

 Patton & Amassian (82) and Ijy Landau (54, 55). 



Despite these reservations, the bull^ar pyramid is 

 the best level at which to study pyramidal tract func- 

 tion. At the suprabulbar and the cord level, and even 

 in the decussation (Bo), the tract is hopelessly con- 

 taminated with other functional systems. 



PYR.AMID.^L deficit; SECTION OF PVR.AMID 



The full extent of the bulbar pyramids can readily 

 be exposed by reflecting the trachea and pharynx and 

 removing the basiocciput. One or both pyramids can 

 then be cut; care must be taken to avoid injury to 

 the overlying basilar artery and its branches.'' 



The effects of experimental pyramidotomy have 

 been studied in the rat (7), dog (92, 94), cat (50, 68, 

 75, 99, 100), monkey (89, 92, loi, 103), and chim- 

 panzee (103). L'nilateral lesions cause contralateral 

 paresis, varying in severity according to the species. 

 In rats, the flexor muscles are particularly affected, 

 but the paresis diminishes, although it does not disap- 

 pear, in 2 to 3 weeks. In cats and dogs, the hind limbs 

 are more severely affected than the forelimfis. Walk- 

 ing is not permanently abolished, but there are 



' The proximity of the lemniscus makes depth of section crit- 

 ical, and dimpling of tissue under the knife causes uncertainty. 

 By any technique, the lemniscus probably suflTers some insult; 

 but the difficulty can be diminished by passing a fine suture 

 under the tract and gently pulling the free ends, passed through 

 a fine glass tube held against the pyramidal surface, until the 

 suture cuts through the tract. Slightly modified, the same tech- 

 nique can be used to transect the bulb for experiments in 

 which it is desired to have only the pyramids in continuity (52). 



Striking disturbances in precise locomotory move- 

 ments, e.g. walking a narrow track or ladder. The 

 contact and visual placing reactions are diminished 

 or abolished. The paretic limb exhibits decreased re- 

 sistance to passi\e extension; resistance to passive 

 flexion appears to be increased but may result from 

 fle.xor hypotonicity (99). 



In the monkey and the chimpanzee, the effects of 

 pyramidotomy are more severe (103). The chief de- 

 fect is the contralateral paresis involving the muscula- 

 ture from the neck down. This affliction is more 

 severe in the chimpanzee than in the rnonkey; indeed, 

 in the former the relatively stereotyped movements of 

 progression appear to be somewhat impaired, al- 

 though they are not abolished. In neither animal is 

 paralysis ever so grave that the affected limbs are 

 useless, but there is severe poverty of movement and 

 loss of such fine movements as apposition of thumb 

 and index fiinger in grooming or manipulating small 

 objects, individual movements of digits in exploring, 

 and elevation of one shoulder in evacuating a gorged 

 food pouch. This deficit has been observed to last up 

 to 4 years and thus may be considered permanent. 

 Tower (103) describes such animals as follows. 



"The usage which survives, be it posture, progres- 

 sion, fighting, or reaching-grasping, is stripped of all 

 the finer ciualities which make for aim, precision and 

 modifiability in the course of execution. These re- 

 maining stereotyped performances are useful still, but 

 they are by no means the skilled performances of the 

 intact animal. Inasmuch as the residual performances 

 may require the most intense voluntary attention for 

 their successful employment, as happens after bilat- 

 eral pyramidal lesion in the adult monkey, the condi- 

 tion cannot be called a complete voluntary paresis. 

 In other words, extrapyramidal action from the cortex 

 may be employed quite as voluntarily as pyramidal 

 action. The selective destruction is of the least stereo- 

 typed, most discrete, moxements or elements in 

 movement." 



Associated w ilh the paresis is a hypotonia, reduced 

 resistance to passive manipulation, which is somewhat 

 more proininent in the monkey than in the chim- 

 panzee. Unilateral lesions affect the abdomen and the 

 extremities most severely. The leg suffers more than 

 the arm, although with bilateral lesions the hypo- 

 tonia is relatively uniform. At first thought, the rela- 

 tive severity of leg impairment following unilateral 

 lesions is surprising because fiber counts indicate a 

 reduction of 50 per cent after the lateral corticospinal 

 tract has descended below the cervical enlargment 

 (107). Since the contribution to arm segments is 



