How our memories become a 'treasure-trove'

At one time or another in our life, all of us are confronted with the most fundamental question of “who am I?” Do our memories make us who we are?  When our memories are lost we are thrown into a realm of confusion about ourselves. From this we can safely conclude that our memories are a significant part of our identity. But have you ever wondered about the genesis of these memories? How is it that certain memories are more profound than others? Isn’t it puzzling how the same brain that can sometimes forget the simplest of things can also remember certain incidents that haunt us for the rest of our lives!

Such complex questions have got many inquisitive neuroscientists thinking for over centuries now. Let us join in this quest and find what’s going on, as it involves our memories too.

How are memories formed? When rodents move around in space, individual neurons known as ‘place cells’ get stimulated, in a manner similar to how Google Maps encodes the location of a place. These place cells are found in a part of the brain called the Hippocampus. Similarity to the shape of a sea-horse (genus: Hippocampus) gives the human hippocampus its name. Human hippocampus is critical for episodic memories - a very personal, autobiographical recollection of significant events in our past. These memories typically take a form of "what" happened, "where" it happened, and "when" it happened. These episodic memories are the reason why place and time are the first things you think of while recollecting any past personal experience. What do the rodents "place cells" have to do with episodic memory? The maps formed by these "smart neurons" can act as framework for storing significant events in our life in the context of where they happened. This creates a "cognitive map"- a scientific term for the map of our memories in our brain. This explains why we first think of a place or time and then start recalling the details of the event.

Dr. Sachin Deshmukh’s lab at the Centre for Neuroscience in the Indian Institute of Science is on an interesting journey to discover how the brain integrates this information about space and events in order to form a cognitive map- this map is interesting, because it is a gestalt representation: the ability of our minds to perceive something in its entirety, not merely the components in isolation.

 In his words, “The focus of my lab's research is to identify the sources of these two types of information, and to understand how these are synthesized into a gestalt representation of space and memories of significant events.”  His team has been studying the brain structure and function at a range of levels from neurons, to networks of neurons, to neural systems and behaviour, with an interdisciplinary approach. They have recorded activities of neurons in the hippocampus as well as its input to understand the nature of information encoded by these neurons.

His team studies how the lateral and the medial entorhinal cortex (LEC and MEC) enable the hippocampus to perform its role. The entorhinal cortex is the main interface between the hippocampus and the neocortex (the part of the brain associated with a variety of functions including movement, touch, sight and hearing in mammals). It plays an important role in the formation of spatial memories including memory formation, consolidation and memory optimization during sleep. Did you ever think so much work went behind you remembering your first date?

Dr. Deshmukh says, “We have shown that LEC and MEC provide complementary representations of space to the hippocampus. While MEC represents the animal's current location based on ‘path integration’ computations,LEC derives spatial information from landmarks, in addition to encoding non-spatial information about those landmarks”. Path integration calculates the position of the animal in its environment based on its speed and direction. Unless kept in check, this path integration process in MEC is prone to accumulate errors. This is where the space represented by LEC comes to the rescue.

Unravelling such secrets of memory formation, Dr. Deshmukh has expanded the field of neuroscience. When asked about the implications of his research Dr. Deshmukh said, “Similar combination of path integration and intermittent landmark based correction is used in robotic navigation. Current research in the lab is advancing this picture by explicitly looking for the intermittent transmission of information from LEC to the hippocampus”. This could therefore mean advancement in the exciting field of robotics as well.

These findings are in their initial stages, but can obviously be applied in order to develop smarter tools for navigation and storing memory based on the integration of space and events. This work could potentially shed light on the reasons behind confusion about location, time and events seen in hippocampal deficit disorders like Alzheimer’s disease. Though it is too early to be certain, the understanding of network level changes could possibly lead to early diagnosis as well as possible treatments.

The novel work done by his team has given us a better insight to the workings of the brain during memory formation and consolidation. Dr. Deshmukh’s lab is definitely a place to look out for exciting innovations in the future as he so very eloquently puts it, “I see that these findings will give rise to larger questions about neuronal function. I see my lab bridging the molecular-systems divide and the sensory-cognitive divide to answer questions about how the brain works.” This would definitely mean a breakthrough in the field of neuroscience and us getting the true picture of that which makes us who we are.

 

Contact: Dr. Sachin Deshmukh <sachin@cns.iisc.ernet.in>