Abnormal c-Fos expression in TetTag mice containing fos-EGFP.

Molecular and genetic techniques now allow selective tagging and manipulation of the population of neurons, often referred to as "engram cells," that were active during a specific experience. One common approach to labeling these cells is to use the transgenic mouse (TetTag). In addition to tagging cells active during learning, it is common to examine the reactivation of these cells using immediate early gene (IEG) expression as an index of neural activity.

Phasic locus coeruleus activity enhances trace fear conditioning by increasing dopamine release in the hippocampus.

Locus coeruleus (LC) projections to the hippocampus play a critical role in learning and memory. However, the precise timing of LC-hippocampus communication during learning and which LC-derived neurotransmitters are important for memory formation in the hippocampus are currently unknown. Although the LC is typically thought to modulate neural activity via the release of norepinephrine, several recent studies have suggested that it may also release dopamine into the hippocampus and other cortical regions.

Septo-hippocampal dynamics and the encoding of space and time.

Encoding an event in memory requires neural activity to represent multiple dimensions of behavioral experience in space and time. Recent experiments have explored the influence of neural dynamics regulated by the medial septum on the functional encoding of space and time by neurons in the hippocampus and associated structures. This review addresses these dynamics, focusing on the role of theta rhythm, the differential effects of septal inactivation and activation on the functional coding of space and time by individual neurons, and the influence on phase coding that appears as phase precession.

Amnesia for context fear is caused by widespread disruption of hippocampal activity.

The hippocampus plays an essential role in the formation and retrieval of episodic memories in humans and contextual memories in animals. However, amnesia is not always observed when this structure is compromised. To determine why this is the case, we compared the effects of several different circuit manipulations on memory retrieval and hippocampal activity.

Acute Disruption of the Dorsal Hippocampus Impairs the Encoding and Retrieval of Trace Fear Memories.

A major function of the hippocampus is to link discontiguous events in memory. This process can be studied in animals using Pavlovian trace conditioning, a procedure where the conditional stimulus (CS) and unconditional stimulus (US) are separated in time. While the majority of studies have found that trace conditioning requires the dorsal segment of the hippocampus, others have not.