The other day I was running an errand in Kensington Market. It was my first time in months – which was weird, because I used to live there (Market purists will demand I specify: I lived two minutes away).
The place han’t changed at all. There was the same smell of fish at the corner of Augusta and Baldwin, the same quasi-creepy storefronts I’ve always wondered about but never entered, and the same fruit stand where I used to buy tulips every week for three dollars. Everything storefront was overwhelmingly familiar. But the Market as a neighbourhood didn’t feel like it was mine anymore.
It’s surprising how quickly a neighbourhood will abandon you. When I walk by my old apartment, I can still call up every memory of living there, yet something about the place has changed. I navigate the neighbourhood differently, because I no longer have the reference point of where I live. When I’m in Kensington now, I’m not just a two-minute walk from home anymore.
Our brain creates internal maps of the places we’ve known. For example, if you were to divide your current space (a room, or outdoor area) into a grid, one group of neurons will fire only when you’re in a specific square of that grid. As you move to a different square, another group of neurons will fire. These are called grid cells, and were discovered in 2005. In a similar way, another type of neuron will fire when you’re close to the border of your environment.
Taken together, these neurons are called “place cells” – which are best described as your brain’s metric for physical space. They tell you where you are in your environment, and keep track of where you’ve been. So far, scientists have only identified place cells in rats and mice, but they likely also exist in humans in a region in and around the hippocampus (which, by the way, is vaguely shaped like a seahorse).
The hippocampus also happens to be one of the key spots for processing and storing memories – so it’s interesting that spatial navigation and memory take up much of the same neural real estate. Maybe it would explain the memory rush that comes from returning to a familiar place. The memory itself and the place in which you encoded the memory are intuitively bound together – not just in our minds, but even in our brain anatomy.
In fact, in humans, the left hippocampus in particular is involved with memory for personal events, spatial navigation, and creating a narrative. I’m speculating now, but maybe in some way, this part of the brain helps to bring the story to the places we’ve been.
Even in rats, the place cells (which are monitored via electrodes implanted into the brain) respond to specific combinations of spatial navigation and goal-directed behaviour. Those neurons will fire to a particular behaviour (like foraging for food), when that behaviour involves a particular direction of movement in a given space.
Of course, the opportunities for poking electrodes into a human’s brain are understandably quite rare. But if you could’ve recorded my place cells a year ago in Kensington Market, you probably would have seen some neurons lighting up on my way South to the fruit stand to buy tulips, and others lighting up on my way home walking North after a coffee on Augusta.
Now that home is a different place – this time 47 minutes away and not just two – my brain has had to remap the market. The landmarks are different and my reference points are off. While the place is entirely the same, I can’t help but smell the fish market, or see the quasi-creepy storefronts, or buy the three-dollar tulips a little bit differently.
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