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Trace effects after polarization of single cortical units recorded extracellularly

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After-effects arising after polarization of single units of the sensorimotor cortex of unanesthetized rabbits through the extracellular recording microelectrode were studied. In most neurons, after both excitatory and inhibitory currents, prolonged changes in activity were observed, consisting of an increase or decrease in discharge frequency compared with initial levels. With currents up to 20–30 sec in duration the mean duration of the after-effect is similar to the polarization time, while with prolonged (5–10 min) polarization it does not exceed 2–3 min. The after-effects are particularly well marked in neurons exhibiting significant changes in discharge frequency against the background of polarization, either as an increase (gradual activation or “escape from inhibition”) or as a decrease (adaptation or gradual inhibition). No significant changes in after-effects are found after administration of nembutal (30–40 mg/kg). The results are discussed in the light of data obtained by means of intracellular microelectrodes (28). It is suggested that after-effects following extracellular polarization, like those following intracellular, are due not to circulation of impulses in neuron networks, but to adaptive properties of the excitable membrane. The two types of effects after switching off an extracellular current in one direction are explained by assuming that such a current has a twofold action, depolarizing some parts of the membrane and hyperpolarizing others.

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Voronin, L.L., Solntseva, E.I. Trace effects after polarization of single cortical units recorded extracellularly. Neurosci Behav Physiol 3, 1–8 (1969).

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  • Sensorimotor Cortex
  • Discharge Frequency
  • Nembutal
  • Extracellular Recording
  • Gradual Activation