Local Generation and Propagation of Ripples along the Septotemporal Axis of the Hippocampus

A topographical relationship exists between the septotemporal segments of the hippocampus and their entorhinal–neocortical targets, but the physiological organization of activity along the septotemporal axis is poorly understood. We recorded sharp-wave ripple patterns in rats during sleep from the entire septotemporal axis of the CA1 pyramidal layer. Qualitatively similar ripples emerged at all levels. From the local seed, ripples traveled septally or temporally at a speed of ∼0.35 m/s, and the spatial spread depended on ripple magnitude. Ripples propagated smoothly across the septal and intermediate segments of the hippocampus, but ripples in the temporal segment often remained isolated. These findings show that ripples can combine information from the septal and intermediate hippocampus and transfer integrated signals downstream. In contrast, ripples that emerged in the temporal pole broadcast largely independent information to their cortical and subcortical targets

Large-scale, high-density (up to 512 channels) recording of local circuits in behaving animals

Monitoring representative fractions of neurons from multiple brain circuits in behaving animals is necessary for understanding neuronal computation. Here we describe a system that allows high channel count recordings from a small volume of neuronal tissue using a lightweight signal multiplexing head-stage that permits free behavior of small rodents. The system integrates multi-shank, high-density recording silicon probes, ultra-flexible interconnects and a miniaturized microdrive. These improvements allowed for simultaneous recordings of local field potentials and unit activity from hundreds of sites without confining free movements of the animal. The advantages of large-scale recordings are illustrated by determining the electro-anatomical boundaries of layers and regions in the hippocampus and neocortex and constructing a circuit diagram of functional connections among neurons in real anatomical space. These methods will allow the investigation of circuit operations and behavior-dependent inter-regional interactions for testing hypotheses of neural networks and brain function

A toolbox of Cre-dependent optogenetic transgenic mice for light-induced activation and silencing

We report on wide-field optically detected magnetic resonance imaging of nitrogen-vacancy centers (NVs) in type IIa polycrystalline diamond. These studies reveal a heterogeneous crystalline environment that produces a varied density of NV centers, including preferential orientation within some individual crystal grains, but preserves long spin coherence times. Using the native NVs as nanoscale sensors, we introduce a three-dimensional strain imaging technique with high sensitivity (<10[superscript -5] Hz[superscript –1/2]) and diffraction-limited resolution across a wide field of view.Allen Institute for Brain ScienceHoward Hughes Medical Institut

BDNF Boosts Spike Fidelity in Chaotic Neural Oscillations

Oscillatory activity and its nonlinear dynamics are of fundamental importance for information processing in the central nervous system. Here we show that in aperiodic oscillations, brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family, enhances the accuracy of action potentials in terms of spike reliability and temporal precision. Cultured hippocampal neurons displayed irregular oscillations of membrane potential in response to sinusoidal 20-Hz somatic current injection, yielding wobbly orbits in the phase space, i.e., a strange attractor. Brief application of BDNF suppressed this unpredictable dynamics and stabilized membrane potential fluctuations, leading to rhythmical firing. Even in complex oscillations induced by external stimuli of 40 Hz (γ) on a 5-Hz (θ) carrier, BDNF-treated neurons generated more precisely timed spikes, i.e., phase-locked firing, coupled with θ-phase precession. These phenomena were sensitive to K252a, an inhibitor of tyrosine receptor kinases and appeared attributable to BDNF-evoked Na(+) current. The data are the first indication of pharmacological control of endogenous chaos. BDNF diminishes the ambiguity of spike time jitter and thereby might assure neural encoding, such as spike timing-dependent synaptic plasticity