30 research outputs found
On information metrics for spatial coding
The hippocampal formation is involved in navigation, and its neuronal activity exhibits a variety of spatial correlates (e.g., place cells, grid cells). The quantification of the information encoded by spikes has been standard procedure to identify which cells have spatial correlates. For place cells, most of the established metrics derive from Shannon's mutual information (Shannon, 1948), and convey information rate in bits/s or bits/spike (Skaggs et al., 1993, 1996). Despite their widespread use, the performance of these metrics in relation to the original mutual information metric has never been investigated. In this work, using simulated and real data, we find that the current information metrics correlate less with the accuracy of spatial decoding than the original mutual information metric. We also find that the top informative cells may differ among metrics, and show a surrogate-based normalization that yields comparable spatial information estimates. Since different information metrics may identify different neuronal populations, we discuss current and alternative definitions of spatially informative cells, which affect the metric choice
Theta Phase Modulates Multiple Layer-Specific Oscillations in the CA1 Region
It was recently proposed that fast gamma oscillations (60--150 Hz)
convey spatial information from the medial entorhinal cortex (EC) to
the CA1 region of the hippocampus. However, here we describe 2
functionally distinct oscillations within this frequency range, both
coupled to the theta rhythm during active exploration and rapid eye
movement sleep: an oscillation with peak activity at ~80 Hz and
a faster oscillation centered at ~140 Hz. The 2 oscillations are
differentially modulated by the phase of theta depending on the CA1
layer; theta-80 Hz coupling is strongest at stratum lacunosum--
moleculare, while theta-140 Hz coupling is strongest at stratum
oriens--alveus. This laminar profile suggests that the ~80 Hz
oscillation originates from EC inputs to deeper CA1 layers, while
the ~140 Hz oscillation reflects CA1 activity in superficial layers.
We further show that the ~140 Hz oscillation differs from sharp
wave--associated ripple oscillations in several key characteristics.
Our results demonstrate the existence of novel theta--associated
high-frequency oscillations and suggest a redefinition of fast
gamma oscillations
Spike Avalanches Exhibit Universal Dynamics across the Sleep-Wake Cycle
Scale-invariant neuronal avalanches have been observed in cell cultures and
slices as well as anesthetized and awake brains, suggesting that the brain
operates near criticality, i.e. within a narrow margin between avalanche
propagation and extinction. In theory, criticality provides many desirable
features for the behaving brain, optimizing computational capabilities,
information transmission, sensitivity to sensory stimuli and size of memory
repertoires. However, a thorough characterization of neuronal avalanches in
freely-behaving (FB) animals is still missing, thus raising doubts about their
relevance for brain function. To address this issue, we employed chronically
implanted multielectrode arrays (MEA) to record avalanches of spikes from the
cerebral cortex (V1 and S1) and hippocampus (HP) of 14 rats, as they
spontaneously traversed the wake-sleep cycle, explored novel objects or were
subjected to anesthesia (AN). We then modeled spike avalanches to evaluate the
impact of sparse MEA sampling on their statistics. We found that the size
distribution of spike avalanches are well fit by lognormal distributions in FB
animals, and by truncated power laws in the AN group. The FB data are also
characterized by multiple key features compatible with criticality in the
temporal domain, such as 1/f spectra and long-term correlations as measured by
detrended fluctuation analysis. These signatures are very stable across waking,
slow-wave sleep and rapid-eye-movement sleep, but collapse during anesthesia.
Likewise, waiting time distributions obey a single scaling function during all
natural behavioral states, but not during anesthesia. Results are equivalent
for neuronal ensembles recorded from V1, S1 and HP. Altogether, the data
provide a comprehensive link between behavior and brain criticality, revealing
a unique scale-invariant regime of spike avalanches across all major behaviors.Comment: 14 pages, 9 figures, supporting material included (published in Plos
One
Hippocampal 4-Hz oscillations emerge during stationary running in a wheel and are resistant to medial septum inactivation.
Recent studies described 2-4 Hz oscillations in the hippocampus of rats performing stationary locomotion on treadmills and other apparatus. Since the 2-4 Hz rhythm shares common features with theta (5-12 Hz) oscillations-such as a positive amplitude-running speed relationship and modulation of spiking activity-many have questioned whether these rhythms are related or independently generated. Here, we analyzed local field potentials and spiking activity from the dorsal CA1 of rats executing a spatial alternation task and running for ~15 s in a wheel during the intertrial intervals both before and after muscimol injection into the medial septum. We observed remarkable 4-Hz oscillations during wheel runs, which presented amplitude positively correlated with running speed. Surprisingly, the amplitude of 4-Hz and theta oscillations were inversely related. Medial septum inactivation abolished hippocampal theta but preserved 4-Hz oscillations. It also affected the entrainment of pyramidal cells and interneurons by 4-Hz rhythmic activity. In all, these results dissociate the underlying mechanism of 4-Hz and theta oscillations in the rat hippocampus
Hippocampal 4-Hz oscillations emerge during stationary running in a wheel and are resistant to medial septum inactivation
Recent studies described 2–4 Hz oscillations in the hippocampus of rats performing stationary locomotion on treadmills and other apparatus. Since the 2–4 Hz rhythm shares common features with theta (5–12 Hz) oscillations—such as a positive amplitude-running speed relationship and modulation of spiking activity—many have questioned whether these rhythms are related or independently generated. Here, we analyzed local field potentials and spiking activity from the dorsal CA1 of rats executing a spatial alternation task and running for ~15 s in a wheel during the intertrial intervals both before and after muscimol injection into the medial septum. We observed remarkable 4-Hz oscillations during wheel runs, which presented amplitude positively correlated with running speed. Surprisingly, the amplitude of 4-Hz and theta oscillations were inversely related. Medial septum inactivation abolished hippocampal theta but preserved 4-Hz oscillations. It also affected the entrainment of pyramidal cells and interneurons by 4-Hz rhythmic activity. In all, these results dissociate the underlying mechanism of 4-Hz and theta oscillations in the rat hippocampus
Relationship between running speed and the instantaneous amplitude of 4-Hz and theta oscillations before and after muscimol injections.
(A) Scatter plots of running speed and the instantaneous amplitude of 4-Hz oscillations before and after muscimol from individual rats. The upper, middle, and lower panels show data from rats A498, A543, and A943, respectively. The individual rho- and p-values are A498: Pre, rho = 0.39, p (TIF)</p
Hippocampal 4-Hz oscillations emerge during wheel but not maze running.
(A) Schematic representation of the U-shaped maze (gray) coupled to a running wheel (red, upper). A typical example of the spatial trajectory of a rat on the maze (black) and in the wheel (red, lower). (B) Spectrograms showing energy at 0–12 Hz frequencies during representative maze and wheel runs (left and right, respectively, upper). Notice that only wheel running exhibits prominent energy at 4 Hz and 8 Hz frequencies. Raw LFP and 3–5 Hz band-filtered signals (gray and cyan, respectively, middle), and the instantaneous running speed at the same maze and wheel runs as above (lower). (C) Autocorrelograms of LFP signals across 304 runs at the maze and the wheel (left and right, respectively). Gray traces represent the average autocorrelograms across trials. Interpeak intervals were 145 ms (6.8 Hz) during maze runs and 320 ms (3.1 Hz) during wheel runs. (D) Average power spectra from LFP obtained during maze and wheel runs (black and red, respectively, n = 304 trials). Solid lines depict the mean and dashed lines depict ± SEM. (E) Boxplot showing the distribution of power in the 3–5 Hz band during maze and wheel runs (left, p < 0.01, WSR test). Distribution of power in the theta (6–10 Hz) band during maze and wheel runs (right, p < 0.01, WSR test). ** indicates p < 0.01 at the WSR test.</p
Peak frequency within 4-Hz and theta bands during maze and wheel runs.
(A) Peak frequency within the 4-Hz band during maze and wheel runs (left, p (TIF)</p