Changes in synaptic efficacy, including long-term potentiation (LTP) and long-term depression (LTD), provide mechanisms for experience-induced plasticity and play a key role in learning processes. Some types of learning (e.g., motor learning, fear conditioning) result in LTP and/or LTD-like changes at synapses. Here, rats learned to discriminate two visual stimuli, P+ and P2, indicating the presence and absence, respectively, of a hidden escape platform in a Y-shaped water maze. Following task acquisition, trained rats showed larger amplitude of visually evoked potentials (VEPs) in V1 to both stimuli encountered during training relative to novel stimuli. Training also resulted in a facilitation of LTP induced by theta-burst stimulation (TBS) of thalamic afferents to V1 with no effect on depression induced by low-frequency stimulation (LFS). Visual VEP enhancement and increased LTP both required that visual stimuli carried some significance to the animal, as both effects were absent in control rats exposed to the same visual stimuli in the absence of pairing with platform location. Together, these experiments show that visual experience can result in a stimulus-selective response enhancement and an increase in the synaptic modification range of V1 synapses, providing a novel example of metaplasticity in circuits of the adult cortex.

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The rat visual system is structured such that the large (>90 %) majority of retinal ganglion axons reach the contralateral lateral geniculate nucleus (LGN) and visual cortex (V1). This anatomical design allows for the relatively selective activation of one cerebral hemisphere under monocular viewing conditions. Here, we describe the design of a harness and face mask allowing simple and noninvasive monocular occlusion in rats. The harness is constructed from synthetic fiber (shoelace-type material) and fits around the girth region and neck, allowing for easy adjustments to fit rats of various weights. The face mask consists of soft rubber material that is attached to the harness by Velcro strips. Eyeholes in the mask can be covered by additional Velcro patches to occlude either one or both eyes. Rats readily adapt to wearing the device, allowing behavioral testing under different types of viewing conditions. We show that rats successfully acquire a water-maze-based visual discrimination task under monocular viewing conditions. Following task acquisition, interocular transfer was assessed. Performance with the previously occluded, "untrained" eye was impaired, suggesting that training effects were partially confined to one cerebral hemisphere. The method described herein provides a simple and noninvasive means to restrict visual input for studies of visual processing and learning in various rodent species.

This cross-sectional study examines out-of-pocket costs for the treatment of invasive breast cancer in employer-insured women younger than 65 years.