Famous German philosopher Immanuel Kant (1724-1804) considered perception of place as the most critical of innate functions in human beings through which external world could be perceived.
Psychologist Edward Tolman from USA (1948) first published the concept of cognitive map in the brain which formed a subject of intense speculation and enquiry in mid twentieth century. However, it was Sturmwasser who for the first time implanted micro electrodes within the brain and studied the activities which opened a much feared and difficult research opportunities to relate deep anatomical locations and functions of the brain .
Space and Time are arguably the two most important informations we need for our existence. No wonder we have a system in place in our brain much like a GPS (Geo- Positional system) in a vehicle which guides us while we cover distances.
Professor John O’Kaffe as well as a husband -wife team of Professor Edward Moser and May -Britt Moser were chosen for the Nobel prize for physiology or Medicine medicine in the year 2014 for their seminal contribution in advancing scientific knowledge by putting forward a concrete anatomical and physiological basis within the brain which find out how we orient and navigate from one place to another.
Professor O’Kaffe from university college of London gave the first breakthrough in 1971 by locating ‘Place cells ‘within the hippocampus of a rat which helped form a map within the brain.
In 2005, Moser couple team published a landmark paper which located’Grid cells’ and its functions in movements of the rat in experimental set up and subsequently in humans and advanced the understanding in this little chartered field of cognitive neurosciences.
O’Keefe and Dostrovsky in 1971 first published the physical existence of ‘Place Cells ‘in the dorsal hippopotamus by looking at the active neural networks while rat was made to walk within an enclosed area. Individual “Place cells “ were active only when the animal was in a particular place . By altering the place of the rat systematically O’Keefe could ascertain that these neurones were very specific in locational function giving a physical substrate for spatial navigation .
Moser couple while working for their PhD in Oslo started focusing on the detailed role of hippocampus in spatial navigation and found that it is separate area behind the hippocampus known as “Entero -Rhinal Cortex “ which has a very close associative role in navigation as there are yet another group of cells known as ‘Grid cells ‘which influence the ‘place cells ‘through a part of brain known as dentate gyrus and adjoining CA3 area of the hippocampus .
These ‘Grid Cells ‘were differently functional cells with unusual firing pattern. They were active in multiple places in the open area forming nodes of extended hexagonal grids, much like a Beehive.
Grid cells in the same area of inner enterorhinal cortex fire with the same spacing and orientation of the grid but in different phase so that all the points are covered together simultaneously.
The fact that grid formation was not seen in any other parts of the brain Mosers concluded that it provides solution to the measuring movement distances and added a measure to the spatial maps of the hippocampus. It was also found that there were two other cells known as “Border cells “and “Head cells “with additional functions.”
Border cells “become active when they encounter boundary (periphery)of the area and “Head cells” become active while looking for direction and behave much like a compass.
Interestingly In the 1950s Scoville and Milner (1957) published a report about a patient named Henry Molaison ( HM) whose both hippocampus were removed as treatment for epilepsy following which he suffered severe memory loss and was not able to encode new memory (episodic memory loss ) while he could still retrieve past memories and was unable to orient his movements . it suggested the role of hippocampus in recent memory which also guide movement and navigation in real time .
After memory has been encoded it further goes consolidation of the entire experience eg during sleep. Ensemble recording with Multi electrodes in sleeping animals has revealed how memories of spatial events coded during active navigation are consolidated during sleep in the same representation order. The replay of place cell activity during sleep appears to be memory consolidation process where memory is stored in the different parts of the cortex. In the story of HM he could retain his ability to recall his past memories relatively better because of consolidation of past memory in the different cortex of the brain.
Strange finding of increased hippocampal size of London taxi drivers after their extensive training in years lend credence to the critical role of hippocamaoal foemation in animals and humans alike.
As Brain is the most important organ whose dysfunction makes people functionally disabled in many diseases such as Alzheimer’s or Parkinson’s diseases and in host of degenerative
diseases where their inability to orient and navigate suffers making life miserable ,may soon get a solution with such paradigm shifting fundamental research .
Two other facts come out from the above account that memory functions can be improved by experiences and if it’s repeated such mental exercise may help the memory coding much better.
This is further consolidated by good sleep when memory is relocated in different parts of the brain cortex which last long and for rest of the life time.
The author is former Professor and Head, Dept of Medicine, RIMS. Ranchi and the views expressed in the article are his own.
