A prefrontal cortex alpha/delta switch controls the transition from positive to negative affective states

Abstract

Positive and negative emotional states in rats can be studied by investigating ultrasonic vocalizations (USVs). Positive affect in rats is indexed by 50 kHz hedonic USVs, and negative affect is indexed by 22 kHz aversive calls. We examined the relationship of emotional states in rats using medial prefrontal cortex (MPFC) quantitative electroencephalograms (qEEG) and found that hedonic USVs were associated with active wake qEEG (high alpha/low delta power), and aversive USVs occurred with groggy wake qEEG (low alpha/high delta). Further, alpha frequency electrical stimulation of the MPFC induces hedonic calls and reward-seeking behavior, whereas delta frequency stimulation produces aversive calls and avoidance behavior. The brain region responsible for generating motor output for USVs, the periaqueductal gray (PAG), shows a motor-evoked potential that is temporally locked to the alpha (hedonic) and delta (aversive) motor-evoked potential. Closed-loop alpha frequency electrical stimulation could prevent delta qEEG and aversive USVs. At the neuronal circuit level, the alpha rhythm was associated with synaptic long-term potentiation (LTP) in the cortex, whereas the delta rhythm was associated with synaptic depotentiation (LTD) in the cortex. At the pharmacological level, NMDAR and growth factor modulation regulated these forms of neuroplasticity. At the single neuron level, excitatory neurons show increased activity in response to alpha frequencies and decreased activity during delta frequencies. In humans, the feeling of joy increased alpha and decreased delta power in frontal scalp qEEG, and the opposite response was seen for sadness. Thus, the synchronization of alpha/delta oscillations through the neuronal circuit responsible for emotional expression coordinates emotional behavior, and the switch between active wake/positive affect and groggy wake/negative affect is under the control of an LTP- LTD synaptic plasticity mechanism.