The origin of the occipital lambda wave in man.

The relationship between occipital lambda waves, saccadic eye movements, and pattern reversal visual evoked potentials (VEPs) has been investigated in 23 normal control subjects and 24 patients with suspected multiple sclerosis (MS). The VEP, electro-oculogram (EOG) and lambda waves were recorded similarly in both groups. The lambda waves were averaged, using pre-defined points in the saccadic eye movements for synchronisation. A comparison was made between the VEP and lambda waves recorded in patients with delayed VEP and in patients with a 'W'-shaped VEP morphology. In the normal subjects, the VEP and lambda waves recorded in response to full-field stimulation were compared with those recorded using a stimulus devoid of foveal pattern. In addition, the lambda waves from the control group were averaged according to different criteria, dependent on the presence of a secondary, corrective saccade. A hypothesis for the generation and transmission of lambda waves has been established. It is proposed that there are 2 different types of lambda wave. The first is generated as a result of retinal afferent activity due to the return of normal visual sensibility in the peripheral visual field, following its suppression during the saccadic eye movement. This activity is transmitted via the faster conducting Y fibres in the optic nerve. The second lambda wave results from the retinal afferent volley caused by the release of suppression of the central visual field, conducted via the slower X fibres in the optic nerve.