Estimating extracellular spike waveforms from CA1 pyramidal cells with multichannel electrodes.

Extracellular (EC) recordings of action potentials from the intact brain are embedded in background voltage fluctuations known as the "local field potential" (LFP). In order to use EC spike recordings for studying biophysical properties of neurons, the spike waveforms must be separated from the LFP. Linear low-pass and high-pass filters are usually insufficient to separate spike waveforms from LFP, because they have overlapping frequency bands.

Tracheotomy improves experiment success rate in mice during urethane anesthesia and stereotaxic surgery.

Urethane anesthesia is frequently used for acute experiments on small rodents in physiology and neuroscience. Severe respiratory distress is a common side-effect of urethane anesthesia in many strains of mice. Associated complications interfere with completion of experiments, and as a consequence more animals must be sacrificed.

Microstructure of a spatial map in the entorhinal cortex.

The ability to find one's way depends on neural algorithms that integrate information about place, distance and direction, but the implementation of these operations in cortical microcircuits is poorly understood. Here we show that the dorsocaudal medial entorhinal cortex (dMEC) contains a directionally oriented, topographically organized neural map of the spatial environment. Its key unit is the 'grid cell', which is activated whenever the animal's position coincides with any vertex of a regular grid of equilateral triangles spanning the surface of the environment.

Spatial representation in the entorhinal cortex.

As the interface between hippocampus and neocortex, the entorhinal cortex is likely to play a pivotal role in memory. To determine how information is represented in this area, we measured spatial modulation of neural activity in layers of medial entorhinal cortex projecting to the hippocampus. Close to the postrhinal-entorhinal border, entorhinal neurons had stable and discrete multipeaked place fields, predicting the rat's location as accurately as place cells in the hippocampus.

Hippocampal neurons responding to first-time dislocation of a target object.

To examine how hippocampal neurons respond to a mismatch between retrieved and actual experience, we trained rats to find a hidden platform at a particular location in an annular watermaze and then moved the platform. Several cells that were silent at the new platform location before the move fired vigorously when the rat found the goal. The new activity was paralleled by reduced discharge in a subset of simultaneously recorded interneurons.

Place cells and place recognition maintained by direct entorhinal-hippocampal circuitry.

Place cells in hippocampal area CA1 may receive positional information from the intrahippocampal associative network in area CA3 or directly from the entorhinal cortex. To determine whether direct entorhinal connections support spatial firing and spatial memory, we removed all input from areas CA3 to CA1, thus isolating the CA1 area. Pyramidal cells in the isolated CA1 area developed sharp and stable place fields.