Teaching NeuroImage: Temporal Intermittent Rhythmic Delta Activity

Temporal intermittent rhythmic delta activity (TIRDA) is characterized by rhythmic slowing at 1-3.5 Hz over the temporal region, typically during drowsiness and light sleep (eTable 1, eFigure1).e1 It often occurs with temporal epileptiform discharges, although TIRDA can occur in isolation. Irrespective of its co-occurrence with temporal epileptiform discharges, TIRDA is considered a reliable interictal marker of temporal lobe epilepsy.1 This pattern is believed to be primarily associated with epileptogenesis in the mesial temporal lobe2; however, it may originate from lateral temporal or orbitofrontal cortices.e2,e3 Because TIRDA does not have the characteristic epileptiform morphology of spikes and sharp waves, it may be considered an epileptiform equivalent. In a critical care setting, this finding is referred to as temporal lateralized rhythmic delta activity (LRDA).e4