Lambda waves: a remarkable electroencephalographic record of a normal physiological phenomenon

Resumo

Lambda waves are triangular-shaped monophasic electropositive sharp transients, occurring over the occipital or parieto-occipital regions . They correspond to benign variants on electroencephalogram (EEG) and, sometimes can be misinterpreted as epileptiform activity due to their sharp contour . They are usually symmetrical and time-locked to saccadic eye movements of awake subjects, during visual exploration, especially of a complex scene, and disappearing when eyes are closed and in sleep . Their name is derived from the resemblance of the wave to the Greek capital letter lambda (λ)⁴. The expression of these waveforms seems to be secondary to a functional activation of networks probably localized within parieto-occipital regions³. Their generators, however, are not fully elucidated. The first reports about the presence of lambda waves date back to the early 1950s, suggesting that it is a phenomenon possibly associated with the presence of epilepsy or some organic brain disease¹. Roth and Green¹, however, were the first to obtain evidence that it was a normal physiological phenomenon. Here we present a remarkable 13-year-old boy waking EEG sample, with a normal background tracing and no history of neurological or other diseases. Note the blocking reaction of the occipital alpha rhythm with eye opening, and the appearance of positive, monophasic, triangular-shaped waves about 3.0 seconds later, initially to the right and then bilaterally, corresponding to lambda waves (figures 1 and 2). After eye closure, the lambda waves disappear, and we can observe the return of a slightly accelerated posterior alpha rhythm (the alpha squeak effect).