(A) Experimental schematic. Left: The binocular segment of V1 in one hemisphere was imaged on day 1 to determine responses to ipsi and contralateral eye stimulation. Middle: 24 hr later the contralateral eye was stimulated with high contrast drifting gratings of 16 orientations for 1 hr starting 30 min after the administration of neuromodulator agonist (isoproterenol, 15 mg/kg, i.p.; Ro 60–0175, 10 mg/kg, i.p). Right: after 24 hr in the dark V1 was imaged again. (B,C) Pairing with the 5HT2c agonist Ro 60–0175 specifically reduces the response to the stimulated eye and reduces the contralateral bias. (B) Example experiment. Left: vasculature pattern of the imaged region used for alignment. Scale bar, 1 mm. Middle: magnitude map of the visual response from the eye contralateral [C] or ipsilateral [I] to the imaged hemisphere. Gray scale (bottom): response magnitude as fractional change in reflection x104. Arrows: L, lateral, R, rostral. Right: histogram of ocular dominance index (ODI) in illustrated in the number of pixels (x-axis: ODI, y-axis: number of pixels) (C) Summary of changes in response amplitude of the conditioned contralateral eye (left) and the non-conditioned ipsilateral eye (middle) as well as the change of ODI (right) before (b) and after (a) conditioning. Thin line: individual experiments; thick line and symbols: average ± s.e.m. (D,E) Pairing with the β-adrenergic agonist isoproterenol enhances the response to the stimulated eye and the contralateral bias. Example experiment in D, summary results in E, conventions as in B, C. (E,F) Visual stimulation alone does not affect either the visual response or the contralateral bias. Example experiment in E, summary results in F, conventions as in B,C.