The Link That Allows Memory to Shape the Way We See the World

Perception is so often treated as a realm of philosophical bar tricks. You know: what is real anyway, man? Gravity hills, size-swapping quarters, moonrises, and Tea Party politics: perception is an almighty source of the subjective manipulation of reality, of mind games in which the outside necessarily becomes a force/function of the inside. It’s also the locus of roughly half of the stupid shit said around drunken/stoned/mushroomed campfires, and the basis for more philosophical (and occasionally pseudoscientific) factions than I care to think about. Someone with a graduate degree that taught at least one class at an almost Ivy League university explained to me once that perception completely diminished mathematics as a foundation of reality, and physics along with it, just because we as perceiving creatures can perceive things differently than what they are. “IRL” is, therefore, unattainable and, with it, science. Brutal.

That’s an extreme and way oversimplified notion and I think most serious philosophers have managed to extricate their considerations of perception from scientific realism—the notion that science can draw a reality more or less independent of perception—at least in way that doesn’t put serious philosophy constantly at odds with scientific discovery. The guys on NPR/Stanford University’s “Philosophy Talk” are pretty good at the difficult art of staying within science while exploring things that might necessarily be outside of it, or at least noting “science” as a force capable of demarcating the boundaries of philosophical discussion. But only if the need should arise.

What makes the science/philosophy relationship really interesting in terms of perception is just how quickly scientific knowledge of the brain is advancing. As we get better and better at explaining how and why the brain perceives the world (perhaps differently than the real world), as “fooling ourselves” gets mapped to neurological processes by theory and experimentation, then “the doors of perception” look less like a fruitful intellectual retreat away from scientific reality and more like, well, scientific reality.

This is all worth keeping in mind as perception gets peeled away by discoveries like this one today: researchers at Cold Spring Harbor Laboratory have for the very first time glimpsed one of the brain feedback circuits in charge of perception. Specifically, the circuit links the olfactory bulb (in mice) with areas much deeper in the brain that are responsible for cognition and memory production. So, as a mouse takes a sniff of the world, that incoming information is mediated by memory-linked granule cells that actually inhibit the full force of the smell input. So as the mouse takes a whiff, its memories shape how that whiff is perceived. This is the very first time the granule cells have been observed at work in an awake animal.

"The granule cells provide a way for the brain to 'talk' to the sensory information as it comes in," explains Cold Spring’s Stephen Shea. "You can think of these cells as conduits which allow experiences to shape incoming data." It makes sense. Smells, particularly for a creature highly dependent on them, are vastly complex, possibly too complex to make good or at least efficient use of in unmediated form. Shea adds, "… granule cells might help animals to emphasize the important components of complex mixtures."

If the brain isn’t associating information with a smell, that smell isn’t worth very much. And any brain has over time smelled lots of smells and linked them up with important knowledge, like, say, one particular component of a smell relating to a memory of a predator. Such a relationship should increase the “salience” of that smell, making it feature more prominently in the entire smell mixture (of maybe urine, pine trees, dirt, and assorted wood). If I were driving my truck one day smelling the usual smells of wet dog and top secret hidden rotting apples, and the mixture began to feature even the slightest smell of gasoline too, I might smell the gas with an intensity not matched by the actual smell mixture reality. This phenomenon of perception would likely have its roots in one of my old cars' full-on blowing up on the highway due to a gas tank leak. The brain is good at stuff.

Shea even allows himself a little philosophy (at least sounding like philosophy) in his study’s press release: “The interplay between a stimulus and our expectations is truly the merger of ourselves with the world. It exciting to see just how the brain mediates that interaction." I like that. We’re in a feedback loop with the world, as long as we can generate memory.

Or so it would seem. A 2006 study (and several before it) found that visual perception in a batch of memory-impaired humans was unhindered, while a different study found a high prevalence of time perception disorders in memory-impaired schizophrenic patients. The memory/perception research well is actually far deeper than the scope of this post, but it’s still worth wondering what would happen if your granule cells were just shut off completely and your sensory inputs had no access to the brain’s memory files. Would we be approaching a world not subject to tricks of perception? What would that look/smell/feel like? Time for some shrooms and a campfire, I guess.