Article Figures & Data
Figures
- Fig. 1.
A, Scheme of the setup arrangement for optical recordings. The size of the field of view as well as filter settings and wavelengths are indicated. B, Snapshots of the response to a single electrical stimulus applied to the white matter (guinea pig visual cortex slice) and recorded using differential fluorescence (df) (left) and ΔF/F (right). The responses were almost identical. The color scale fromblue to red represents a 0–0.48% change in ΔF/F and a 0–255 change in df. Layers are indicated and are based on Nissl-stained sections. C, Comparison of fluorescence values with intracellular membrane potential. Fluorescence (recorded as df) and membrane potential (Vm) in response to a single stimulus to the white matter are shown. Top left, A snapshot of activity (layers and stimulating electrode position are indicated) at 8.4 msec after the stimulus was applied to the white matter;circles represent three arbitrary points where pixel values were obtained. Intracellular recording was from position 2, as indicated by the pipette. Top right, Time course and amplitude of fluorescence values obtained at points 1–3. Bottom left, Synaptic responses at three differentVms to single stimuli applied to the white matter. Bottom right, A comparison of the time course and amplitudes of light and of a cell at rest (−77 mV) recorded from position 3. D, Depopolarizing and hyperpolarizing pulses applied to the same cell as in C at various times during the recording to verify that input resistance and action potential characteristics are unaltered and the slice is healthy. The cell depicted is a regular spiking cell from upper layer 6, with an input resistance of 39 MΩ. Scale bar: B, C, 1 mm.
- Fig. 2.
Optical recordings are primarily generated by orthodromic activation. Snapshots of the optical responses to a single stimulus under control conditions (left) show that the response was almost completely abolished after 30 min of perfusion in a medium in which Ca2+ was substituted with Mg2+ (right). Cortical layers and the position of stimulating electrodes are indicated.
- Fig. 3.
A, Spatiotemporal patterns of activation resulting from electrical stimulation of the white matter. Optical recordings from guinea pig visual cortex are shown. Time is indicated in milliseconds after the stimulus, and the position of the stimulating electrode is indicated as well. The cortex is positioned with layer 1 on the top and layer 6 on thebottom. The color scale for fluorescence intensity is arbitrary between 0 (blue) and 255 (red).B, Activation profiles after a single electrical stimulus was applied to the white matter. A visual cortex slice is shown. Top left, A snapshot of activation att = 8.4 msec; layers are indicated. Bottom left, Temporal evolution (x-axis) of activation along a vertical line from layers 1–6 (y-axis). The overlying white lineis the summation of pixel values across time (from leftto right) and shows maxima in layers 2 and 3 with a second peak in infragranular layers. Right, Temporal evolution of the activity along a line of pixels parallel to the pial surface within layers 2 and 3 (top) and layer 6 (bottom). Space is represented from left(L) to right(R) of the slice (x-axis); time after stimulation is indicated on the y-axis. Profiles show not only the extent and velocity of propagation but also the duration of the activation of any given pixel.
- Fig. 4.
A, Spatiotemporal characteristics of activation depend on the frequency of stimulation. Snapshots at 7.2 msec after stimulation during the first (left) and fifth (right) stimuli during trains at 10 (top row) and 40 Hz (bottom row) are shown. The color code for intensity ranges from 0 to 255. Responses to the first stimulus were identical at both frequencies. The response to the fifth stimulus did not change when stimulation was at 10 Hz; in contrast, the activation area became smaller and the response amplitude became higher during stimulation at 40 Hz. B, Temporal evolution of the spatiotemporal properties of activation during repetitive stimulation (arrowheads). Activation profile (as in Fig.3B) across layers 2 and 3 in a visual cortical slice. Distance is indicated on the y-axis, and time is indicated on the x-axis. Activation spanned the entire length (∼2.2 mm) of the profile for each stimulus at 10 Hz but shrunk progressively to ∼1 mm during stimulation at 40 Hz.
- Fig. 5.
Spatiotemporal aspects of activation with two electrodes. A slice from the visual cortex was stimulated with two electrodes in the white matter separated by 1.5 mm. The 3-D snapshots illustrate the evolution of the optical response for the 10th stimulus in a train at 10 Hz (top) and 40 Hz (bottom). The responses to the 10th stimulus delivered by each electrode and then the two simultaneously are illustrated. During stimulation at 40 Hz, the activated areas remain segregated. The position of stimulating electrode is indicated.
- Fig. 6.
Pixel values and intracellular recordings during stimulation at different frequencies. Fluorescence values (LIGHT) and intracellular recordings (Vm) were obtained from areas 1 and 2 (dotted lines) during stimulation at 10 and 40 Hz (A1 and A2, respectively, inVm). Bottom right, Comparisons of the first (blue dot) and the last (red dot) of the responses during the trains at the two frequencies are superimposed. B, Cell from position 2 inA2 (arrow). Increasing the intensity of stimulation (from bottom up) triggered responses to all stimuli at 40 Hz. C, Different cells showing long-lasting inhibition triggered by a 40 Hz stimulation.
- Fig. 7.
Membrane polarization reveals frequency-dependent depression of EPSP. A cell recorded intracellularly from the column above the stimulating electrode is shown.A, Electrical stimulation at 40 Hz was delivered to the white matter while changing the Vm of the cell with DC. Traces are displaced artificially for clarity. Vm is indicated. B, Detail of the responses from A, as indicated by theblack bar. C, Detail from the first, middle, and last synaptic responses from trains in A andB. Vertical dotted lines indicate the peak of the EPSP and IPSP, respectively. Horizontal dotted lines are the most depolarized and hyperpolarizedVms because of DC injection.D, Superimposition of the first and last responses (dotted line, scaled to match amplitude of the first response). The last response lacks the EPSP and consists almost exclusively of an inverted IPSP. E, Comparison of the train of responses with response to a single stimulus; the time course of the response to a single shock matches the underlying shape of the train.
- Fig. 8.
Spatiotemporal properties of activation after a single stimulus were altered by local injection of bicuculline.Left, Snapshots of the control response to a single stimulus applied to the white matter; time after stimulus is indicated on the left. Middle, Pattern of propagation after local injection of bicuculline (dotted circle) in position b. Right, Pattern of propagation after local injection of bicuculline (dotted circle) in position c. Values from pixels located in positions a(blue), b (red), andc (green) along the path of propagation are plotted on the right. Note that the pixel values are plotted against the 0–255 color scale represented on the left. Activation invaded areas farther away from the stimulation site according to the location of the bicuculline injection.
