Figure 1.

Experimental paradigm and alignment of probes. (A) LFP obtained from one channel positioned approximately 800 μm below the surface of the gray matter during a single stimulation trial. The red curve presents triggers used for forepaw stimulation. The evoked response appears shortly after each forepaw stimulus pulse. (B) Precise localization of laminar probes relative to the cortical surface: high-resolution image showing the part of a laminar probe close to the surface of cortex. Gray regions and dark curves around the probe are gray matter and pial blood vessels, respectively. Four contacts can be observed above the cortical surface, as indicated by the orange arrow. In this experiment and all other experiments conducted to create the prototypical CSD response presented in (D), we used linear probes with 32 contacts densely spaced at 50 μm intervals covering layers 1–5. (C) The mean CSD response obtained from one run immediately after the image presented in (B) was acquired. The dark horizontal lines mark the approximate depth of the borders between the cortical layers, labeled on the right. Note that in this experiment we used a linear probe with 32 contacts densely spaced at 50-μm intervals covering layers 1–5. CSD values are in micro-Amperes per cubic millimeter. (D) The spatiotemporal pattern of mean CSD responses, used as a template for localizing CSD responses relative to the cortical surface. CSD responses from 12 runs in 4 animals were aligned relative to the cortical surface as determined by their corresponding images of contacts above the surface. The image represents the average CSD response computed following this alignment procedure. The prototype pattern used to align the results from the other experiments was extracted from within the dark rectangle. (E) A 50-μm-thick section of the brain cut from the recording site shown in (B) and stained with Cresyl violet. The image to the left shows a lesion induced through the bottom-most contact (red arrow), traces left by the probe (blue arrow), and delineation to the cortical layers. The image to the right presents the position of all 32 contacts spaced at 50-μm intervals, including the 4 observed above the cortical surface (orange arrow). (F) CSD responses averaged over forepaw stimulations in a single run. The horizontal and vertical axes represent the time from stimulation in milliseconds and the cortical depth in millimeters. The highest dark horizontal line marks the cortical surface based on the spatiotemporal covariance computed on the right. CSD values are in micro-Amperes per cubic millimeter. The image to the right presents spatiotemporal covariance as a function of time and space. The maximal covariance is marked with a white cross. The position of the cortical surface relative to the maximal covariance is marked with a horizontal dark line.