Lambda waves: incidence and relationship to photic driving

The earliest studies on lambda waves in the 1950s postulated a relationship with the photic driving response. Intracranial depth electrode studies from the 1960s showed generators for lambda waves and the occipital driving response to be different but both originating from the posterior hemisphere. Use of computer averaging techniques in the 1980s found these two cerebral responses to be similarly affected by certain diseases. We examined the incidence of lambda over a wider range of ages than previously studied, and also evaluated for a statistical correlation between lambda and occipital driving. Three hundred sixty-seven conventional EEGs were prospectively collected and analyzed. Each record was interpreted for the presence of lambda waves, photic driving, and epileptiform discharges. The incidence of lambda waves, photic driving and epileptiform discharges was 76%, 85%, and 23%, respectively. The incidence of lambda and photic driving exhibited age-dependent characteristics. The amplitude and duration of lambda waves also exhibited age-dependent characteristics. A strong correlation existed between the presence of lambda waves and photic driving (p< 0.001). No significant correlation existed between epileptiform discharges and either lambda waves or photic driving. The strong correlation between the presence of lambda waves and the occipital photic driving response suggests the possibility a common region in the brain needs to be functionally activated in order to express these waveforms.