Functional deficits in V1 of amblyopic cats
K. E. Schmidt1,2, R. A. W. Galuske2, W. Singer2
Introduction: Early convergent squint frequently results in permanent visual deficits in one eye referred to as amblyopia. Electrophysiological recordings attribute the deficits to disturbed neuronal interactions in V1 or higher cortical areas. In the present study we investigated the modulation of responses in V1 to gratings at different spatial frequencies and orientations with optical recording of intrinsic signals.
Methods: Monocular orientation preference maps were recorded optically at spatial frequencies between 0.1 and 2.0cyc/deg in cats with surgically induced early convergent squint. Steady state visual evoked potentials (VEP) were recorded at different spatial frequencies (0.1 to 3.5cyc/deg) to monitor visual acuity development.
Results: When VEPs revealed no relative amplitude (RA) differences between the eyes, orientation maps were equally modulated for both eyes over all spatial frequencies. Cats with significant RA reduction in the VEPs of one eye had well modulated orientation maps for both eyes at low spatial frequencies (0.4-0.7cyc/deg). However, the modulation depth was on average lower for the weaker eye. At higher spatial frequencies (0.7-2.0cyc/deg) maps disappeared completely for the weaker eye while orientation domains could still be activated through the stronger eye.
Conclusion: These data reveal a correlation between the loss of visual acuity in amblyopia as assessed by VEPs and the level of neuronal activation as seen by optical recording of intrinsic signals. In addition, the results suggest that amblyopia is associated with altered intracortical processing already in V1.
2MPI für Hirnforschung, Deutschordenstr. 46, D-60528 Frankfurt/M, Germany, 1Zentrum für Augenheilkunde, Johann-Wolfgang-Goethe-Universität, Theodor-Stern-Kai 7, D-60596 Frankfurt/M.