Retinal ganglion cell dysfunction in humans following post-geniculate lesions: specific spatio-temporal losses...

Nasal and temporal hemifield (14 x 24 degrees) pattern electroretinograms (PERGs) were recorded in eight patients (age range: 21-72 years) suffering from different post-geniculate lesions (documented by CT scan and/or MRI of the brain) and homonymous hemianopia at visual field testing. In total eight age-matched normal subjects served as controls. PERGs were elicited by alternating, sinusoidal gratings (90% contrast), whose spatial and temporal characteristics, 6 Hz-5 c deg-1 and 15 Hz-0.58 c deg-1, were chosen to enhance the relative contributions of parvo- (P) and magno- (M) retinal ganglion cell (GC) subsystems, respectively. Amplitudes and phases of the Fourier analyzed PERG 2nd harmonics were measured. In normal subjects, PERG amplitudes to 15 Hz-0.58 c deg-1, but not those of the 6 Hz-5 c deg-1 stimuli were on average larger (P < 0.05) in nasal than in temporal hemiretinae. In hemianopic patients, PERG amplitudes of 6 Hz-5 c deg-1 stimuli were on average reduced (P < 0.05) in the hemiretinae corresponding to blind hemifields, in comparison to those in the hemiretinae corresponding to functional hemifields. No differences between hemiretinae were observed for responses of the 15 Hz-0.58 c deg-1 stimuli. In both normal subjects and patients, average PERG phases did not differ between hemiretinae, while changing significantly (P < 0.01) across stimulus conditions. The PERG naso-temporal asymmetries observed in normal subjects are consistent with the reported asymmetries in GC density observed histologically (Curcio & Allen. (1990). Journal of Comparative Neurology, 300, 5-25). The results in patients indicate that the PERGs to specific spatio-temporal stimuli (i.e. of relatively low-temporal and high-spatial frequency), presented in the hemianopic field, are reduced in amplitude. This suggests, in agreement with the experimental findings in monkeys (Cowey & Stoerig. (1991). Trends in Neuroscience, 14, 140-145), that retrograde trans-synaptic dysfunction of P-GCs, with relative sparing of the M-subsystem, may occur in humans following lesions of post-geniculate pathways.