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Does the thought of your first kiss still bring you goose bumps or does the memory of a traumatic experience still give you the same rush of anxiety that you experienced before? That’s because the brain pathway that links external events to an internal emotional state involves different parts of the brain to form a single memory. This was demonstrated by researchers from the RIKEN-MIT Center for Neural Circuit Genetics, who also showed that positive or negative emotional valence of memory can be reversed during later memory recall.The study, published in, was conducted by Dr. Susumu Tonegawa and his team. They wanted to know how brain regions like the hippocampus and amygdala were involved in forming memories and if the emotional valence was stored in the same part of the brain as the memory of an event that caused the emotion.

Valence is a psychological term used to describe the intrinsic attractiveness (positive valence) or averseness (negative valence) in response to an event or object.' Both the hippocampus and the amygdala are considered critical for memory formation. We wanted to know whether the memory engram was free to associate with positive or negative valences or whether it was fixed with respect to emotion,' said Roger Redondo, who along with Joshua Kim is co-first author of this study, in a. 'We also wanted to know at what point in the circuit the valence is assigned to the engram, in the hippocampus or the amygdala.'

Quick facts: Location: Part of Limbic System, at the end of the hippocampus; Function: Responsible for the response and memory of emotions,.

The experiments were conducted on mice. They were placed in a novel chamber and divided into two groups.

One group received mild shock on their foot while the other group was allowed to socialize with a female mouse. So the mice formed memories of fear and pleasure. Using biomarkers, the scientists genetically labeled neurons that were active during the formation of either memory. The team then used optogenetics to activate the same set of neurons. Optogenetics uses light sensitive microbial ion channels to manipulate neural activity.

The activated neuron can be controled using light delivered by an LED or laser.When the neurons were activated, the mice showed the same response as they did when they experienced the event. In other words, depending on the valence of the initial experience, the researchers could judge from the mouse's behavior whether the activated memory was a fearful one or a rewarding one, displayed by the mice when they avoided or were attracted to a particular location in the chamber.' If our technology drives memory engrams, it should work independently of whether the valence is negative or positive,' Redondo explained. 'We wanted to show that the memory reactivation was not restricted to fear memories, as we had used in the past.' Next, the team wanted to find which part of the brain stored memory of an event and its emotional valence. For this, they had to switch the valence of memories in mice from negative to positive and vice versa. To do this, the mice were given a new experience of the opposite valence while the researchers simultaneously activated the original memory in either the hippocampus or the amygdala.As a result, the memory engram stored in the hippocampus could change its valence.

So the mice who had earlier received foot shocks were no longer fearful when recalling that experience, while mice that originally socialized with a female now showed fear. The valence of the memory engram in the amygdala, on the other hand, could not be altered.With this, the researchers concluded that memories of either emotion can be reversed in the hippocampus. But the amygdala carries only positive or negative memory and cannot interchange. This study reveals an unanticipated flexibility in brain circuits during memory formation for emotional events.This research could be a stepping stone to develop psychological interventions in people suffering from depression or post-traumatic stress disorder, where negative emotional valence can be reversed to positive valence.

Hippocampus, region of the that is associated primarily with. The name hippocampus is derived from the Greek hippokampus ( hippos, meaning “horse,” and kampos, meaning “sea monster”), since the structure’s shape resembles that of a. The hippocampus, which is located in the inner (medial) region of the temporal lobe, forms part of the limbic system, which is particularly important in regulating emotional responses. The hippocampus is thought to be principally involved in storing long-term memories and in making those memories resistant to forgetting, though this is a matter of debate. It is also thought to play an important role in spatial processing and navigation. Anatomy of the hippocampusThe anatomy of the hippocampus is of chief importance to its function. The hippocampus receives input from and sends output to the rest of the brain via a structure known as the entorhinal cortex, which is located beneath the anterior (frontal) region of the hippocampus.

The hippocampal formation itself is composed of several subregions, which include the cornu ammonis (CA1–4), the dentate gyrus, and the subiculum. Principal neural circuitsThe subregions of the hippocampus are connected by two principal neural circuits: the trisynaptic circuit and the monosynaptic circuit. The trisynaptic circuit forwards information from the entorhinal cortex to the dentate gyrus via the perforant path, which perforates through the subiculum. Information then flows from the dentate gyrus to CA3 via the mossy fibre pathway (so named for the extensive branching of its ).

Finally, information flows from CA3 to CA1 along bundles of axons known as Schaffer. The circuit is completed by outbound projections to the subiculum and the entorhinal cortex. The monosynaptic input bypasses the dentate gyrus and CA3 and instead transmits information directly from the entorhinal cortex to CA1.

Sources of inputThe hippocampus receives input from modulatory systems, including, and systems. It also receives cholinergic input (responds to the neurotransmitter ) from the medial septum, which regulates the hippocampal physiological state. The medial septum is involved in setting one of the critical oscillatory rhythms in the hippocampus, the theta rhythm. Abolishing that region or the associated theta rhythm interferes with hippocampal function. Functions of the hippocampusThe two most-influential theories for hippocampal function are related to space and memory. The spatial was supported by the discovery in 1971 of cells in the hippocampus that fired bursts of when a specific locations in space, or “place fields.” That suggested that the hippocampus was a sort of device used by the brain for mapping layouts of the. Data supporting that idea came from later virtual navigation studies in humans, which suggested a strong association between the hippocampus and spatial navigation.

The memory hypothesis originated in 1957 and was supported by studies and observations in which hippocampal removal resulted in a loss of the ability to form new memories, particularly fact- and event-related (declarative) memories.Although there is near universal agreement among scientists that the hippocampus is important for memory, the exact processes by which the hippocampus supports memory are subject to much debate. Some studies suggest that the hippocampus binds items and into unified experiences and stores them.

Other studies suggest that the hippocampus is preferentially involved in conscious recollection, or the experience of mental time travel during recall. Still other studies suggest that the hippocampus is able to support rapid learning by reducing interference among similar memories (for example, where a person parked his or her car today versus yesterday). Some theories of hippocampal function treat the hippocampus as an index (much like an index at the end of a book) that binds together elements of an experience but does not store the experience itself. The latter is assumed to be stored in a distributed fashion throughout the brain, while the hippocampus is assumed to possess an index of that distributed code.There is disagreement about whether long-term memories eventually become independent of the hippocampus, with the cortex being sufficiently able to support recall.

That is known as the standard model of systems consolidation. The major competing theory, multiple trace theory, suggests that the hippocampus continues to be needed for long-term recall of episodic (context-rich) memories but not for semantic or gist memories. Finally, hippocampal structure, function, and connectivity are not uniform along its longitudinal axis. The anterior hippocampus is preferentially connected to the and orbitofrontal cortex and is thought to be involved principally in the regulation of emotion. The posterior hippocampus is preferentially connected to the retrosplenial and posterior parietal cortices and is thought to be involved principally in and spatial processing.