Amplitude, frequency, and phase analysis of hippocampal theta during sensorimotor processing in a jump avoidance task

Abstract

In the current study, rats implanted with hippocampal recording electrodes were trained to avoid shock in a jump avoidance task, using three separate heights, 28, 33, and 38 cm. The objectives were to measure the progression of Type 2 (immobility-related) hippocampal theta amplitude and frequency recorded during jump avoidances at each of the levels, and determine if there was a consistent relationship between the phase of the Type 1 (movement related) theta jump wave and the moment of movement initiation at each of the jump heights. The results demonstrated that the immobility period prior to the execution of the jump could be divided into two components: a sensory processing period and a movement preparation period. Comparing these two periods, average amplitudes were higher while frequency remained relatively constant during the sensory processing period. During the movement preparation period there was a negative correlation between amplitude and frequency: amplitude declined rapidly and frequency increased rapidly. During the execution of the jump, theta amplitude (Type 1) and frequency were positively correlated, both reaching peak values. The separate analyses of the individual jump heights provided further support for the precise relationships between theta parameters and the magnitude of the required movements. A significant phase preference was demonstrated for the highest jump height, with movement initiation occurring around the trough of theta recorded from the stratum moleculare of the dentate region. The findings supported the conclusion that the generation of hippocampal theta band oscillation and synchrony was related to sensorimotor processing and integration.