EXPERIMENTALLY DERIVED CORRELATES BETWEEN ECG AND STEADY CORTICAL POTENTIAL

Abstract

Steady transcortical potential and the usual electrocorticogram were recorded simultaneously under a variety of exptl. conditions, and the correlations observed. For recording steady cortical potential a chopper was used which was placed across a pair of leads to the usual electroencephalograph, and calomel half-cells were used as electrodes. The observations were made on a series of 20 rabbits. In the absence of exptl. variations designed to effect a change in usual cortical activity the steady voltage across the cortex usually remains stable over the period of several hrs. required to complete an expt. Asphyxia always produces a significant change in steady potential consisting of a positive followed by a negative deflection of significant duration. A brief positive steady potential change occurs as an after-effect of the primary visual response, and a more prolonged one accompanied by cortical paroxysm may be excited by repetitive stimulation in the thalamus. Sufficiently strong surface-positive polarization leads to the development of high voltage paroxysm which is accompanied by a significant positive change in steady potential. Surface-negative polarization applied during such a paroxysm most frequently terminates it. Surface-negative polarization of the resting cortex resulted either in no change or in suppression of electrocorticogram. Residual negativity persists for several minutes after such surface-negative polarization, and may end in a positive shift. As that shift occurs brief paroxysmal bursts occur in the electrocorticogram. In further polarization studies it was shown that the initial surface-positive phase of the diphasic primary visual response is accentuated during surface-negative polarization, the following surface-negative phase by surface-positive polarization. Despite residual negativity or positivity after the current is broken, the form of the response rapidly . returns to its prepolarization state. It. is concluded that the relocation of electrical charges at the superficial and deep ends of the cortical pyramids is a significant factor in bringing about alteration in steady potential levels. To the extent that correlations were possible between steady potential changes induced by experimental variations and changes in electrocorticogram, the data supports the view that change in the state of polarization may affect significantly the level of cortical excitability.