Spectral correlation of action potential firing rates after hypoxic-ischemic brain injury

During recovery from hypoxia-ischemic (HI) injury microelectrode recordings of multiple action potentials from thalamus exhibit periodic oscillations. Firing rate variability analysis reveals that spike frequency is periodically modulated by a low frequency oscillation called spindle. This leads to spectral self-coherences among firing rate components during spindle episodes. In an animal model of cerebral injury we monitor neural responses from the VPL (ventral-posterior lateral) thalamic nucleus after 3 min of total asphyxia. Spindling episodes of VPL multiple unit responses appear within the first 5 min of recovery. These spindles modulate the multi-unit activity at the rate of approximately 10 Hz. Interspike intervals (ISI) fluctuate from 2 to 10 ms during these burst periods. Frequency coupling occurs between frequencies in the 100 Hz to 300 Hz range (p<0.01) induced by the spindle envelope. Thus, spectral correlation analysis accurately captures the low frequency modulation of action potentials from a short segment of data.