Ever since her leap to fame as Rachel on the popular TV sitcom Friends, Jennifer Aniston has been one of the most recognisable actresses in the world. Now, scientists believe that the discovery of brain cells responding specifically to pictures of Jennifer Aniston may hold the key to understanding how the brain forms memories.
Imagine walking down a busy street and noticing a friend walking on the other side of the road. Even following just a brief glance from any angle your brain allows you to recognise your friend and conjure up a whole host of memories about that person; including their name, their personality and perhaps something really important you were meaning to talk to them about. This scenario provides a perfect example of how efficient the brain is when it comes to memory storage and retrieval. However, scientists still have a very limited understanding of how all this can occur so quickly and faultlessly.
The idea that single brain cells can respond exclusively to specific objects/people is not a new one. However this idea is not widely accepted in the scientific community. One notable sceptic was Jerry Lettvin, a researcher from Massachusetts Institute of Technology, who argued against the simplification of memory function in the late ‘60s.
Lettvin expressed his criticism of this idea through an example. He described a hypothetical brain cell specialised to respond only to the sight of your grandmother (a ‘grandmother cell’). This cell could then be linked with and activate many other cells responsible for memories of your grandmother such as the smell of her cooking or the sound of her knitting. Through this example Lettvin highlighted a number of problems with such a simple set-up; if the brain did possess a cell to recognise every single object you’ve encountered then surely the brain would run out of space at some point? Moreover, what would happen if you lost one of these cells? Would you be unable to recognise your grandmother any more?
Despite its ridicule, the ‘grandmother cell’ theory has recently been revived by the discovery of single cells in the human brain which respond specifically to recognisable people. These cells were discovered by a team operating in Los Angeles, California led by Rodrigo Quian Quiroga from the University of Leicester who had the unique opportunity of recording from single cells in the brains of awake, behaving humans.
The ability to record single cell activity in awake human patients is clearly very rare. However, the LA team were able to conduct their study using a special group of patients undergoing treatment for severe epilepsy. When a patient with severe epilepsy does not respond to medication, the faulty brain region responsible for seizure generation must be be removed. As this area usually differs between patients, a surgeon will implant an electrode (see left) into the brain which will record electrical activity in various locations and tell the surgeon which area needs to be removed. This allowed Quiroga and his team to record single-cell activity from awake, behaving humans.
They showed these patients many pictures of objects and people in an attempt to discover what these brain cells responded to. In one of their first experiments they found a cell that appeared to respond specifically to pictures of Jennifer Aniston which they later named the ‘Jennifer Aniston cell’.
To ensure that this cell was actually responding to Jennifer Aniston and not some other feature of the pictures they were using (for example, her blonde hair or maybe the contrast of her compared to the background etc) they tested the cell using a huge range of Jennifer Aniston pictures. These included pictures of her face from various angles, her whole body and some of her standing next to (her then husband) Brad Pitt. These pictures were shown to the patient multiple times and mixed in with pictures of other celebrities and family members.
The results were remarkable. The cell did not respond to any other person (around 80 other people were shown) but responded specifically to pictures of Jennifer Aniston. Interestingly the cell did not care whether it was a head shot or a picture of her whole body – two views which, from an image processing perspective, are very different. However, the cell did not like Brad Pitt! Any time a shot of Jennifer Aniston and Brad Pitt together was shown the cell refused to respond. This baffled the researchers. Why would the cell fire specifically to Jennifer Aniston but only when she was on her own?
The answer came when they found that this cell also responded (not as much as to Jennifer Aniston but enough to be significant) to Lisa Kudrow, the actress who plays Phoebe on Friends. Quiroga hypothesised that the cell was not actually responding to a specific person, but instead responding to the ‘concept’ of ‘Rachel from Friends‘. When Jennifer Aniston was shown on her own, the patient was reminded of Rachel and the cell would fire. When Jennifer Aniston was shown next to Brad Pitt, that was Jennifer Aniston the actress and not Rachel, and the cell did not respond. Thus the cell, once thought to be a ‘Jennifer Aniston cell’, became known instead as a ‘concept cell’. These ‘concept cells’ would form a key part of a hypothesis Quiroga was building regarding memory formation.
Recording from new patients, Quiroga and his team found multiple examples of these ‘concept cells’. For example, cells were found which responded to Halle Berry on her own and Halle Berry in costume as ‘Catwoman’ (pictures where her face is almost entirely obscured by the costume). A cell was also seen responding exclusively to either Luke Skywalker or Yoda; a Star Wars concept cell?
To further cement the ‘concept cell’ theory, Quiroga’s team investigated whether these cells would also respond to non-visual methods of triggering these concepts. To do this they used the ‘text to speech’ function on their laptop playing a robotic voice speaking the celebrity’s name. Amazingly, this had the same effect – that is, the cell that responded to pictures of Halle Berry, also responded to the spoken words ‘HALLE BERRY’. The pathways for the processing of visual and auditory information are largely separate and have limited cross-over but somehow, these two types of information are being relayed to one individual cell.
This raises some interesting questions concerning what happens when we form new memories. Imagine for example that you meet a new person and do not catch their name. Your brain will store a visual image of this person, linking it to a ‘concept cell’. Days or weeks later you may then learn the person’s name. Does this mean that this auditory information will create new links, through a completely different pathway, right back to the original ‘concept cell’ for this person?
If correct, this type of specificity in linking parts of the brain together is truly remarkable. Quiroga believes the ‘concept cells’ he has unearthed in these studies represent the building blocks of our memories and are crucial for forming associations necessary for storing and retrieving multifaceted memories. Quite a claim, but he is uneasy about labelling them ‘grandmother cells’ as this simplifies what many believe to be a complex process. The next stage of this research will be crucial as Quiroga aims to investigate how these ‘concept cells’ communicate with each other and how the timing of each cell’s activity may be the key to linking them – and therefore, your memories – together.
All work described here is summarised in the following review by Rodrigo Quian Quiroga (subscription needed):
Post by Oliver Freeman @ojfreeman