FRANK MORRELL 



383 



across the neuronal gap into the isolated region (Fig. 8). Gross electrodes 

 on the slab first recorded volume conducted potentials unaccompanied by 

 unit discharge and then suddenly the slab burst into self-sustained activity 

 which was associated with niassive unit discharge. Since the high imped- 

 ance of the microelectrodc tip precludes recording at any distance, we 

 must conclude that the discharge truly represents ephaptic activation of 

 ganglionic elements within the isolated region. We do not have time here 

 to discuss the physiological properties of isolated, non-epileptic cortex 

 (see references Libet and Gerard, 1939; Bremer, 1941 ; Burns, 1949; Sloan 

 and Jasper, 1950; Bremer and Desmedt, 1958; Torres, Ziegler and Wissof, 



Isolated cortex ^A^/, ' ^^ .,,... . . ■ '- , v - ,vVvl^,> Vi-^s/vys 



Microelecifode 



Normol corte)' _: 



I solo ted' cortex • ^ * ^ .- 1 , , 1 - -> 



Examples of propagation of abnormal discharges to isolated regions. A pledget of metrazol 

 had been placed on the normal cortex 2 cm. distant from the isolated region. The electro- 

 graphic discharge so induced spreads slowly across the cortex and after some delay was seen 

 to invade the isolated region. Micro-electrode tracings are from tungsten electrodes as des- 

 cribed in the text. Calibration is so microvolts and one second for the ink-writer tracings and 

 I second for the oscillograph. 



1958; Morrcll and Torres, 1958; Marshall, 1959). In our own experience 

 we have never been able unequivocally to demonstrate transmission of 

 electrical discharge into completely neuronally isolated (but otherwise 

 normal, i.e. non-cpilcptic) cortex. The ease with which such ephaptic 

 transmission can be demonstrated ni isolated epileptic cortex makes it 

 clear that the increased excitability or irritability has persisted in the 

 cellular elements of the mirror region despite the fact that the spontaneous 

 manifestation of this irritability was abolished by the neuronal isolation. 

 We believe this to be crucial observation because it demonstrates that the 

 mirror focus is a region which has not only 'learned' to behave in terms of 

 paroxysmal discharge, but which 'remembers' this behaviour even after 

 months of inactivity. The isolation experiment has excluded reverberating 



