Changes in evoked brain oxygen during sensory stimulation and conditioning

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Abstract

Platinum electrodes chronically implanted in the thalamic, amygdaloid, tegmental and caudate areas of three cats were used to record the oxygen currents (aO2) in response to novel and repetitious sensory stimuli and during conditioning and extinction.

The oxygen availability in these circulatory beds of the brain was consistently changed by mild sensory stimulation and dramatically changed by conditioning procedures.

In general, brief novel sensory stimuli produced a sharp increase in aO2 followed by a decrease and a gradual recovery over a period of about 1 min, with the response varying somewhat in different parts of the brain. Stimuli of long duration cause a change in aO2 at both the beginning and end of the stimulus.

Monotonous repetition of click and tone stimuli elicited a gradually decreasing response in aO2, so that finally only the basic or background rhythmic variations were apparent. Reintroduction of a novel stimulus, by changing the tone, re-established the original response.

When auditory signals terminating in an electric shock were used to condition the animal, an increase in aO2, found to be highly reproductible, occurred immediately post-stimulus and coincident with the point of electric shock. This post-stimulus response in aO2 persists for some time after the animals cease to show any visible response to the shock-free tone. The decrease in aO2 following this bimodal response was more variable in duration but tended to be present more often in the conditioned animals.

In avoidance conditioned cats, the changes in aO2 associated with the avoidance response were similar to those recorded in the shock conditioned animals but they required a long time to extinguish. The extinction period was often characterized by aO2 responses which, instead of appearing in all electrode areas, sporadically appeared in one area then another, with recovery and post-stimulus phase disappearing first, and co-stimulus response to a certain extent remaining.

The results are discussed in terms of neurogenic, hormonal and metabolic phenomena in the brain cells and circulation.

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    This investigation was supported by Public Health Service Grants MH-08820, HE-03109 and HE-06353.

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