PMC

Single-trial simultaneous depth profiles of the local field potential, V(t), and the current source density, −Δ²V(z, t)/Δz², in response to a looming ball. (A) (Left) Schematic of the location of the two Si-based arrays in dorsal-area D2, one caudal (C) and one rostral (R) relative to the centroid of the 20-Hz response (Fig. E). (Right) Schematic of the Si-based multielectrode arrays through the depth of cortex. (B) Single-trial measurement of the local field potentials at the two locations in A. The 4-s period of the loom is indicated by the thick bar. (C) The current source density, calculated from the data in B. Note that the lower two rostral traces and the lower three caudal traces have been multiplied by a factor of 2.

Comparison between the responses of successive tungsten (W) microelectrode loci vs. the Si-based multielectrode array. The amplitude and time scales are the same for both sets of records. (A) The single-trial local field potential at a series of successive depths, spaced 100 μm apart, observed in response to a step of illumination from a green light-emitting diode (LED), with a center wavelength of 569 nm, delivered through a diffuser to the contralateral eye. The intensity at the eye was approximately 10⁻⁵ W/cm². Each record represents an individual trial. Note the initial negative-going spike (N). The positive step at the onset of stimulation ✶ is an electronic artifact. (B) Simultaneous single-trial measurement of the local field potential from successive depths, obtained with the Si-based array, in response to a step of illumination.

Cartoon of different models for the appearance of phase or timing differences tangential along cortex. Open circles indicate excitable, not necessarily oscillatory, tissue, whereas circles with ≈ indicate local oscillators. For simplicity, only one-dimensional models are shown. Note that phase differences, Δφ, and timing differences, Δτ are related here by Δφ = 2π Δτf, where f is the frequency of the oscillation. (A) A model where the wave motion is apparent and results from a single oscillator that drives adjacent regions of cortex through increasing time delays of Δτ_D. (B) A model where the wave motion originates from the transmission of pulses along a network of cortical neurons. In this example, a single oscillator launches the pulses. The propagation speed is denoted by v, and the distance between spatial loci is denoted by Δx, so that the time delay between loci is Δx/v. (C) A model where the wave motion originates as stable differences in phase among a network of oscillators that interact via weak short-range connections (shown here as only nearest-neighbor connections). The values of the phase shifts depend on details of the neuronal activation and interactions.

Spectral coherence of the current source density between intra- and interradial locations. (A) The magnitude of the coherence between the upper source/sink pairs of the caudal of two Si-based arrays (100 μm and 200 μm in Fig. C) calculated from single-trial data as a function of frequency and time. The temporal window was 1 s and the bandwidth was 4 Hz. (B and C). Detailed view of the coherence calculation in A for the 20-Hz band. Shown is the magnitude, |C(f)|, and phase, arctangent [Im(C(f))/Re(C(f))], for f = 20 Hz. The gray band indicates the period of the looming stimulus. Note the high coherence during stimulation and the phase shift of near π radians between source/sink pairs. (D and E) The trial-averaged (n = 16) magnitude and phase of the coherence for the upper source/sink pairs of the caudally located array. The black line is the mean response, and the gray bands define the standard deviation. (F and G) The trial-averaged magnitude and phase of the coherence for the upper source/sink pairs of the rostral array. (H and I) The trial-averaged magnitude and phase of the coherence between the uppermost sources of the rostral and caudal arrays. Note the significant phase shift of +0.53 radians.

Spatial localization of the visually induced electrical response. The stimulus was a step of illumination from a green light-emitting diode (LED; parameters as in legend to Fig. ). (A) Example of the surface potential in response to a single step. Note the initial negative-going spike (N-potential) and the subsequent fast oscillations that persist for up to 1 s. The epoch marked “window” corresponds to a 0.5-s poststimulus interval. (B) Power spectra of the “window” epoch in A. Note the stimulus-induced peak near 20 Hz, as well as the increased power at lower frequencies compared with a 0.5-s prestimulus window. The bandwidth of the spectral estimate (full width at half-maximal amplitude) was 4 Hz. (C) The locus of amplitudes of the N-potential. The gray-scale contours correspond to fractions of the maximal response. The spatial coordinate system originates at the medial line and the rostral edge of cortex. (D) The locus of response for the 20-Hz oscillatory band. (E) The trial-averaged centroids for the N-potential and 20-Hz oscillation band are shown relative the anatomical border between dorsal regions D1 and D2 (line); n = 6 animals.