One of the things that continually fascinates me about neuroscience is how interconnected everything is in the brain. As I’ve mentioned before on this blog, we’re always using our entire brains. Unless there is serious damage, no part of the brain is ever inactive. Not only does this mean that every part of the brain is essential, but it also means that every part of the brain is interconnected. In order for every part to be firing almost all the time, every part needs to be connected with every other part. Like I wrote in one of my earlier pieces,
“It’s commonly accepted that two neurons are separated by more than four orders of separation. That means you only need to jump across four neurons to reach any other neuron. To put this in perspective: there are roughly seven billion people on the planet and it’s usually said that any two humans are connected by six or seven orders of separation. Imagine every single person you’ve ever met in your life. A single neuron has ten times more connections than that. (A commonly accepted measure is that neurons can have up to 10,000 connections.)”
That’s insane if you think about it! One single neuron has 10 times more connections than you do.
One way this amazing interconnectivity manifests itself is when neuro-scientists try to figure out how the brain remembers where it is in space. It should be obvious, right? For instance, right now I know I’m at Macalester College. Specifically, I’m in Olin-Rice. More specifically, I’m sitting at the round table across from Eric Wiertelak’s office. My legs are crossed, and I’m typing at my computer. My blue water bottle is next to my left hand, and I’ve taken my shoes off. My stocking feet are comfortable against the carpet.
Each layer of knowledge I have about my surroundings is encoded within a different – yet probably similar – pattern of neuronal firing. For instance, my brain probably has a basic, large “Macalester” firing pattern. All of the experiences, memories, people, and events that I have relating to Macalester are tagged with this recognizable pattern. It’s the same with the tag “Olin-Rice” and “the space across from Eric’s office” only the patterns would be different. Each one of these pattern has a huge number and variety of cells firing at the same time. For instance, there are a number of different neurons that scientists have labeled: map cells, place cells, grid cells, the list goes on (you’ll notice that neuroscientists never seem to come up with very original names). All these different cells fire in relation to different things happening. As Moser and Moser write in ‘Mapping Your Every Move,”
“The grid cells in each of the brain’s modules send signals to the place cells in the hippocampus. The combined effect of this grid cell activity creates an activity field in the hippocampus (the part of the brain devoted to memory), the place field. This signaling, in a way, is the next step in the progression of signals in the brain. When the environment changes, the different grid modules react differently to the change – firing at new positions in the environment, and the linear summation (build-up of a lot of neurons firing) activates different place cells in the hippocampus.”
It’s important to remember that these cells (grid and place) are the same type of neuron. The only thing that’s special and different about them is that they happen to be in different places in the brain and have different connections with other neurons. This interconnectivity is what’s really important.
Articles used: Mapping Your Every Move; Evard and May-Britt Moser; March 1, 2014; Cerebrum
Link to article: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4087187/