The physiological effects of monocular deprivation and their reversal in the monkey's visual cortex.

1. 1127 single units were recorded during oblique penetrations in area 17 of one normal, three monocularly deprived and four reverse sutured monkeys. 2. In all animals most cells outside layer IV c were orientation‐selective, and preferred orientation usually shifted from cell to cell in a regular progressive sequence. 3. The presence in layer IV c of non‐oriented, monocularly driven units, organized in alternating right‐eye and left‐eye 'stripes' (LeVay, Hubel & Wiesel, 1975) was confirmed. 4. Early monocular deprivation (2‐‐5 1/2 weeks) caused a strong shift of ocular dominance towards the non‐deprived eye. However, even outside layer IV c, neural background and some isolated cells could still be driven from the deprived eye in regularly spaced, narrow columnar regions. In layer IV c the non‐deprived eye's stripes were almost three times wider, on average, than the deprived. 5. Later monocular deprivation (11‐‐16 months) had no detectable influence on layer IV c but seemed to cause a small shift in ocular dominance outside IV c. Deprivation for 6 1/4 months in an adult had no such effect. 6. After early reverse suturing (at 5 1/2 weeks) the originally deprived eye gained dominance over cells outside layer IV c just as complete as that originally exercised by the eye that was first non‐deprived. 7. The later reverse suturing was delayed, the less effective was recapture by the originally deprived eye. Reversal at 8 weeks led to roughly equal numbers of cells being dominated by each eye; fewer cells became dominated by the newly open eye after reverse suturing at 9 weeks and most of them were non‐oriented; reversal at 38 1/2 weeks had no effect. 8. Binocular cells, though rare in reverse sutured animals, always had very similar preferred orientations in the two eyes. The columnar sequences of preferred orientation were not interrupted at the borders of ocular dominance columns. 9. Even within layer IV c there was evidence for re‐expansion of physiologically determined ocular dominance stripes. After early reverse suture, stripes for the two eyes became roughly equal in width. Possible mechanisms for these changes are discussed.