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B.A. Ekesten, P. Gouras; Long Lasting Responses in the Murine Visual Cortex . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5376.
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© ARVO (1962-2015); The Authors (2016-present)
To understand the functional organization of murine visual cortex.
Single cell impulses are detected by inserting a metal micro–electrode through the dura–covered visual cortex of ketamine/xylazine anesthetized C57/Bl 6 mice, sometimes from two areas simultaneously. The retina of the left or right eye is stimulated with light emitting diodes (370, strong for UV cone opsin; 505 nm, strong for M cone opsin) producing full field stimuli. Eyes are light adapted to suppress rods. Evidence that more than one cone mechanism produces a response is based on selective chromatic adaptation or lack of response univariance; i.e. a response from one cone mechanism to different wavelengths becomes identical at an appropriate energy.
Full field stimuli produce similar responses in all areas of V1, a negative/positive potential with single cell impulses, often of large amplitude. The response is detected at 0.3–0.5 mm below the cortical surface with a latency of about 50 ms. Most areas have inputs from both cone mechanisms with their strengths resembling their retinal distribution. Energy changes seldom produce univariance of single cell responses. A light pulse produces a repetitive series of bursts lasting many seconds, which resembles the spontaneous frequency, when present. Simultaneous recordings from different areas show that the spontaneous frequency is the same across V1. The repetitive responses to light stimulation are in phase with spontaneous discharges in other areas. Comparison of the spontaneous frequency with and without light stimulation reveals that the light driven response entrains the spontaneous frequency.
All areas of V1 respond to diffuse light stimuli, usually through both UV and M cones. A lack of response univariance implies different pre–cortical circuits for these cones. The long lasting, oscillatory response to light stimuli appears to be due to the photic response entraining an inherent spontaneous frequency present in all of these cells. This mechanism provides a means of reverberating evoked responses in visual cortex.
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