SURFACE MOVEMENTS OF FIGURES IN SPONTANEOUS ACTIVITY OF ANESTHETIZED CEREBRAL CORTEX: LEADING AND TRAILING EDGES

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Abstract
A group of 20 figures appearing in the electrical spontaneous activity of the posterior ectosylvian gyrus of a cat at a certain level of nembutal[long dash]dial anesthesia was recorded with an array of 25 electrodes simultaneously. Records were analyzed for the times of occurrence of the sequential positions on the cortex of the beginnings ("leading edge") and the endings ("trailing edge") of the activity at each cortical point as each figure traveled across the array. The figures occurred in a period of about 25 seconds at an average rate of about one figure per second; each figure is a single entity; at one electrode the associated waveform is a single, slow, predominantly surface-positive deflection. This type of activity is characteristic of the posterior ectosylvian region at this level of anesthesia. Positions and times of occurrence of leading edges of all 20 figures were averaged over the whole time of occurrence and over the first 78 msec. of each figure. These results show that there are at least 2 originating zones for the figures: one near the upper end of the posterior ectosylvian sulcus (the anterior origin) and one near or in the posterior suprasylvian sulcus (the posterior origin). The extreme speeds of travel of the edges of the figures fell within the range 0.05-0.36 m./sec., in directions away from the origins. The average trailing edge moved predominantly toward the center and bottom of the active region at speeds within the range of those of the leading edge. The average elapsed time between the arrival of the leading edge and the departure of the trailing edge at each cortical point was calculated and mapped; there is a central zone with a small gradient of duration and a peripheral zone with a large rate of change. The zone of the smaller gradient corresponds to that in which 90% of the figures are contained at the time of their maximum extent. The map of the number of figures whose leading edge first arrived at a given cortical point shows a maximum around the anterior origin. A chart of the number of figures whose trailing edge last departed from a given cortical point shows a maximum at the lower border of the array. A map of the number of figures whose area at the time of maximum extent included a given cortical point shows a maximum in the central part of the active region which includes the anterior origin. From these charts, the behavior of the average spontaneous figure is as follows: (a) it originates either in an anterior origin (most frequently) near the dorsal tip of the posterior ectosylvian sulcus or a posterior one near or in the posterior suprasylvian sulcus; (b) it grows as it moves from the origin toward the center of the upper part of the posterior ectosylvian gyrus (two small figures died before growing); (c) it takes up its maximum included area as it reaches this center; (d) it then moves dorso-ventrally along the center of the gyrus to the lower part of the gyrus. Similar figures can be elicited at the anterior origin by intense, relatively long sounds; trains of clicks so condition the mechanisms generating the spontaneous figures that figures occur only at the anterior origin for the first 500 msec. after click and at the posterior origin for the second 500 msec. All speeds found are in a range similar to that of the cortical surface-positive response of Adrian in intact cortex and of Burns in isolated cortex. A suggestion is made that the anterior origin is connected with the reticular activating system, and the posterior one with the recruiting response system.

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