| Abstract: | Steady potential shifts produced by focused ultrasond were recorded in the cerebral cortex, hippocampus, thalamus, and caudate nucleus. Impulses of 50–100 msec duration were presented at a frequency of 5 and 10 Hz. Negative steady potential shifts were produced in each of the structures investigated, which gradually increased during rhythmic electrical reaction to reach –3 to –7 mV within 10–30 sec, often succeeded by a wave of spreading depression (SD). In each structure analyzed amplitude of SD waves measured 20–30 mV, lasting 30–40 sec in the cortex, the caudate nucleus and the thalamus, and 80–120 sec in the hippocampus. In unanesthetized and lightly anesthetized animals SD waves were on occasions the precursors of convulsive discharges forming under the action of focused ultrasound. Ultrasound at threshold doses proved ineffective for 5–7 min after the occurrence of an SD wave, but again evoked repeated SD waves once the refractory period had ended. Accordingly, local effects produced by focused ultrasound can result in functional blockage of the brain structures due to cortical and subcortical spreading depression.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Institute of Brain Research, All-Union Research Center of Mental Health, Academy of Medical Sciences of the USSR, Moscow. N. N. Andreev Acoustic Institute, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 18, No. 1, pp. 55–61, January–February, 1986. |
