Spatial memory, grid cells and…honeycomb?!

Remember when we talked about memory? One very important aspect you should never forget is that there are many types of memory (stored in different areas of the brain). Today I’d like to discuss a particular and very important type of memory, known as spatial memory. As a matter of fact, I’m going to be even more specific: this article deals with one of the several types of cells involved in spatial memory, which were recently discovered. These were called grid cells (the name is very suggestive, as you’ll see in a few moments).

You may wonder why I chose this topic. Obviously, it is of great interest for many scientists, but to be honest, my own subjectivity played a role in here as well. For those who haven’t met me, you should know this: there is no one in the world less capable of spatial self-orientation than myself! Therefore, when I heard that a young Norwegian couple (the Mosers) won the Noble Prize in 2014 for discovering some neurones specialised in location memory, it came as no surprise that I became extremely curious about their research.

As I mentioned before, grid cells are not the only neurons involved in spatial memory. In the 1970, John O’Keefe discovered navigation in the brain along with the cells that generate this process, known as place cells. These neurons are located in the hippocampus (a structure of the temporal lobe associated with long-term and spatial memory) and appear to code for location, by creating a spatial map of the environment. They are dependent on the motion’s speed and direction.

Grid cells represent a type of place cells, although unlike place cells, they are predominantly found in the medial entorhinal cortex. Some grid cells were also found in the prefrontal cortex, which is involved in forming episodic memory. A quite peculiar characteristic about these neurons is that they fire whenever the subject is at certain locations and these signalling locations form a hexagonal pattern, very similar to a honeycomb (which explains the rather odd image I chose for this article).

This honeycomb-like pattern is not only mathematically precise, but it is also very efficient as it uses a minimum number of grid cells to achieve the highest-possible resolution, thus saving energy.  It was also discovered that the firing patters remain constant during the subject’s movement, regardless its speed or direction. Moreover, unlike the response of place cells, which is based on visual stimuli, the grid cells’ firing is maintained even in the absence of sensory stimuli, thus showing an algorithm based on self-motion. In an interview for Deutsche Welle Magazine, Edvard Moser says: “It is thought that these [grid cells] are part of an internal map that is based on our own movement, so that these cells signal the distances we move and the directions we take”.

The discovery raises scientists’ hopes up in treating neurodegenerative diseases linked to memory, such as Alzheimer’s disease, as it has been demonstrated that the first symptoms of dementia appear in the entorhinal cortex. At the same time, for other people, like me, grid cells may offer an explanation as to why they still can’t find their best friend’s house, after having been there several times.

Articles related to the subject:

 Nature

 New Scientist 

 Deutsche Welle 

Image created by Isuru Priyaranga

Why drugs are actually bad!

We are all well aware of how serious and, unfortunately, wide-spread drug addiction is, yet we don’t actually know what makes people so dependent of a drug after they have started using it. Even more intriguing is why former addicts, who have stopped using drugs for weeks or months, revert back to drug use, knowing full well that the substance they were addicted to in the past pretty much ruined their lives.

As I am sure you expect this article to shed light on the problem, I’m not going to keep you guessing. Two weeks ago, a team of researchers at the Icahn School of Medicine in US published a greatly revealing study in The Journal of Neuroscience. They appear to have found the answer to how cocaine affects decision-making in addicts as well as why abstinent users often choose to start taking cocaine again.

Dopamine is one of the commonest neurotransmitter in our brains. It is involved in many cognitive processes, including prediction and recognition of loss. Therefore, dopamine plays a very important role is some mental and also neurodegenerative diseases, such as schizophrenia (where dopamine levels are overly increased) and Parkinson’s disease (caused by decrease in dopamine secretion in the midbrain and degradation of dopamine receptors).

This recent study shows that cocaine acts on dopamine signalling, influencing the so-called Reward prediction error (RPE). It has been recorded, fallowing neuroimaging and pre-clinical studies, that dopamine signalling is increased in response to an unpredicted reward (which is scientifically referred to as positive RPE) and decreased as a result to a negative outcome or the omission of a predicted reward (negative RPE). The team of researchers demonstrated, therefore, that cocaine reduces the response to unpredicted loss (impaired negative RPE), while leaving the positive RPE almost intact.

In order to obtain these results, the team used 75 subjects, who were divided into two groups: 25 non-cocaine users and 50 cocaine addicts. Moreover, the second group was also divided as fallows: 25 cocaine users who had taken cocaine within 72 hours of the study and 25 cocaine users who had abstained from taking cocaine within 72 hours of the study. All subjects had to play a computer game that involved prediction and guessing.

As you may expect, the non-users responded normally to both unexpected  loss and predicted reward, as well as to predicted loss and unpredicted positive outcome. On the contrary, the cocaine users responded far less to unexpected negative outcome. This means that their brains were reacting less strongly to the negative result of a prediction than the normal subjects’ brains.

Moreover, and this is the most fascinating part, the users who hadn’t taken cocaine within 72 hours, showed deficit in positive RPE, whereas the other addict group (who had consumed cocaine in the previous 72 hours), had unaffected positive RPE, but impaired negative RPE. Also dysregulation in serotonin system in drug addicts might lead to this kind of results (serotonin signalling has been registered in response to negative prediction, in normal brains).

So, to cut the story short and in a more simplified version, if you use cocaine, you are more likely to omit the bad things in your life. But if you take cocaine and then you give up, you get the opposite result: you become less able to enjoy positive aspects. This might account for the fact that people who stopped taking drugs tend to start using them again after rehab. Does this mean we have to become drug addicts? It seems like this is the solution. Well…NO! Definitely not! And I’m not saying this because I might get into trouble for promoting drug use, but there is a very important reason for that. We DO need to anticipate and recognize negative outcomes. This is how all creatures in this world survive. This is how more advances creatures (like humans) are capable of making good decisions and learn from mistakes.

Some might argue, though, that it is preferable to be happy all the time, despite how much you fail and that there is no such thing as actual failure, as it’s all about how our own brains perceive the environment. What do you think? Is this true or not? Either way, I strongly suggest you don’t start using drugs!

The study

Image modified by Isuru Priyaranga

Let’s not forget about memory!

In the previous article we talked about empathy, as the capacity to put ourselves in someone else’s shoes and understand them. We discussed about the structures involved, in a quite simplistic manner, but as it turns out things are not that simple. What makes the brain so fascinating (and hard to study as well) is the fact that each and every process, from the basic to the more advanced ones (like reasoning, planning, decision-making) require the integration of many different structures and other processes, that in turn depend on other processes and so on. A bit confusing, isn’t it? Don’t worry! If you feel lost, then you’re actually on the right track.  

Mirror neurons represent one of the basic keys behind empathy (as presented in the previous article), but they don’t explain the whole picture, though. In order for us to be able to relate to a complete stranger’s situation and feel what he’s feeling, we first need to be able to relate to ourselves. More specifically, our brain should be capable of retrieving something from our own past that is similar or triggers similar emotions to what the stranger is experiencing. (This is, of course, involuntarily and subconsciously.)

That’s where memories come in. Memory is a very common term and almost all the people know what it is about. Or do they? In fact, “memory” is quite ambiguous and imprecise; neuroscientists discuss about “types of memory”. Indeed, there are several categories in which memories are classified (visual-spatial memory, auditory memory, emotional memories, long-term memory, short-term memory – if we focus on duration – and so on). 

To spare us of too much confusion, scientists decided to divide memory into two broad categories: declarative (explicit) and non-declarative (implicit) memory. The first one refers to memories for facts and events and is the conscious component, whereas the second one includes the types of memory that don’t have a conscious component, such as memories for skills and habits, priming, classical conditioning, simple forms of associative learning, as well as simple forms of non-associative learning (habituation and sensitization).

A lot of information to take in, I know. But if you’ve manage to get this far, I promise you won’t be disappointed! The big question that has given scientists a hard time for years was: “Where exactly is memory stored?” Initially it was thought that memory is somehow spread throughout the whole brain. Well…it’s not! And we now know this thanks to one of the most famous patients in the history of Neuroscience, Henri Molaison or H.M., as he is referred to in literature.

H.M. had been suffering from epilepsy his entire life and in 1953 he underwent lobotomy to treat his seizures. Thus, he had a part of the brain removed, which included both his left and right temporal lobes. After the surgery, the epilepsy was gone, but instead something else appeared to have taken its place… H.M. was no longer able to form new memories (anterograde amnesia). To him, every day was like a new beginning: everything he did or learnt, all the people he met the day before, were completely new the day after. At least, he never got bored (which allowed neuroscientists to study this patient his entire life, as he couldn’t recall any of the tests he participated in). 

Interestingly, his old memories (from childhood, for instance) were unaffected and he was even able to learn new things, although he had no recollection o them. Thus, scientists concluded that the temporal lobes and especially the hippocampus were responsible for the formation of long-term declarative memories, but instead this type of memory was stored somewhere else (in the frontal cortex). Also, a different region of the brain is involved with memories for skills and habits (the striatum). Hence, there are specific cortical areas where memories are encoded.

This article is just to give you a bit of an understanding of how the brain deals with basically sorting our entire lives into distinct, separate “folders”, but it’s not even close to covering this whole vast subject. At some point, you might come across another article about a special type of memory that was recently discovered. 

Did memory manage to arouse your curiosity? If so, I’m looking forward to comments.  

P.S. I would like to give very special thanks to Sorin Hornoiu and Isuru Pryiaranga, who created the images for the first article and this one, respectively. I try as much as possible to use original pictures (not downloaded from the internet) and their creative skills really come in handy. 

Empathy and…mirror neurons!

As I am quite sure all of you have watched Titanic at some point in your lives or at least know the story, I’m gonna ask you one simple question? How did you feel when Jack Dawson died at the end of the movie? Did you burst out into tears, did you feel an overwhelming sadness? If the answer is Yes! (and should be, unless you are some socio-paths, heartless people – just kidding, I didn’t cry either!), this article is meant to briefly explain what actually happened in our brain at that time. 

Psychologists would call this empathy. And that’s true. For a few moments you were experiencing what Rose was feeling while she was seeing her lover freezing to death and then drowning. But why did you empathize with a movie character? What do humans empathize at all? It all comes down to neurons. In order to try to understand this complex process that lies behind our ability to put ourselves in someone else’s place, we need to figure out the neurological mechanisms that triggers all this. (This could be a good excuse when someone calls you a wet blanket, for example: ‘It’s not me, it’s my mirror-neurons and oxytocine signalling in the anterior cingulate gyrus’, as you’ll see below) 

Some special motor neurons have been discovered in the frontal lobes of monkeys, that apparently signal both when the animal is performing a particular task and when it’s seeing someone else doing the same thing.They were called mirror neurons.  It’s important to bear in mind: “the same thing”, because for another type of action, other mirror neurons would show activity. Thus, these neurons are highly specific. Evidence of mirror neurons have been recorded in humans as well, using neuroimaging, but there isn’t a 100% certainty they actually exist, as it is in macaques and apes. 

Researchers now believe that mirror neurons (if they indeed exist in humans) are also involved in the development of learning (in particular, in language formation); they also appear to account for the evolution of mankind throughout the history (from homo sapiens to homo sapiens sapiens – around 200,000 years ago – and the development of arts, modern tools, religious beliefs – later on, around 40,000 years ago). Moreover, many scientists see dysregulation in mirror neurons’ activity as a possible cause of autism – one of the primary symptoms of this disease being the incapacity of the patient to relate himself to the exterior world, hence the anti-social behaviour. 

There are many other long-known brain structures which trigger emotions and empathy, such as the anterior cingulate gyrus, the amygdala, the hippocampus, the neurotransmitter oxytocin…But mirror neurons are a quite novel discovery and may set neuroscientists on track to explain complex processes that happen in our brains. Cool, right? 🙂 

This article is not only about mirror neurons, but also about empathy. I put a link to a short video filmed in India, in which a macaque monkey is being resuscitated by another one, after having been electrocuted. Some say this is a clear sign of empathy in animals (at least in the superior ones; also elephants, dolphins have shown many signs of empathy before). Other say it is a normal altruistic behaviour, present in most animals (from insects to mammals). Ethologists and population geneticists refer to altruism as one of the instincts of putting others in your species first in order to assure species’ survival and evolution and is mostly encountered in animals that have lived in groups. 

What do you think? Do some animals empathise or what we might see as an empathic behaviour is nothing more than pure adaptive instinct?

Monkey video

Interesting article about mirror neurons

Article – Empathy brain differences