Sunday, June 15, 2008

Inside A Bear's Brain

Excerpts from an article written by Michael Jamison and published in the Jackson Hole Star Tribune about Dr. George Stevenson, a pioneering neurosurgeon, and his presentation, "Grizzly Bear Brain, Central Nervous System Structures," before a group of Glacier National Park personnel during a seminar in West Glacier, Montana.

"These bears are amazing creatures," Stevenson said. "I believe they have the most impressive olfactory system of any animal on the planet. Their nose is the very best."

Mostly, he was pointing out the snout, a full nine inches of highly evolved scent detection. It is, he said, like no other nose in the world.

A run-of-the-mill dog's sense of smell is roughly 100 times greater than a human's. A good hound dog's nose is perhaps 300 times better.

But a bear's scent system, Stevenson said, is at least seven times better than the hounds. "It's remarkable," he said. "It's how they know the world."

When humans think about their hometowns, they think in terms of visual maps - down this street to that avenue, turn left at the bank, right at the stoplight. But bears don't see thinks that way. To get to their favorite huckleberry patch, they don't follow the trail to the tree with the broken limb, and then turn left at the big mossy rock.

"No, they have an olfactory map."

Take the scent of the trail to the smell of the anthill, then follow the smell of water to the perfume of huckleberries.

It is difficult, Stevenson said, for humans to imagine such a way of knowing, but to bears it's essential.

Each spring, when they emerge from the den, they are literally starving. There's no time to wander around and look for food, to look for tracks in the snow  and to follow them, perhaps, to a protein meal.

"They have to smell food over hugh distances, and go straight to it," Stevenson said, If they can't, they die."

. . . the percentage of a bear's brain devoted to scent is at least five times greater than the percentage of human brain allocated to olfactory systems.

In other words, humans smell in black and white, while bears enjoy the full kaleidoscope.

"A polar bear will walk 100 miles in a straight line to reach a female ready to breed," he said. "That's what the bears nose can do. They smell a million times better than we do."

A human brain weighs in at about 1,500 grams, huge compared to a 450-gram bear brain. And yet our olfactory bulb is the size of a pencil eraser. The bear's is the size of your thumb. That's a lot of smell power for such a small brain.

And even before the brain, he said, the bear's body is built to sniff.

The black pad on the bear's snout, like a dog's nose, is wired with hundreds of tiny muscles. Bears can manipulate their nostrils the way dexterous people control their nimble fingers.

The smells then travel up two 9-inch channels, with hundreds of times the surface area of a human's nose, to a spot where 10 million nerve strands and a billion receptor cells fire electrical signals directly into the brain, through countless tiny pathways and onto the brain's cribiform plate.

The large hippocampus "remember" the scent, adding it to the mental map.

Just imagine the blinding brain punch a blast of pepper spray must deliver to that system.

"It's not just heat and discomfort," Stevenson said. "It actually scrambles the brain."

"They definitely see in color, but not the way we do. We're totally visual. There's no way bears see as well as you and me. I thinks their hearing is quite good. It's nothing compared to that nose, though."

"This is a whole new way of knowing the species," Stevenson says.

"For me, this is absolutely fascinating - like getting inside a bear's head and seeing with his eyes, smelling with his nose. It gives people as idea of how they see us, which is not something people think about very much."

1 comment:

Elle Smith Fagan said...

The bear's head is so large that I wondered about its brain - and your article answered my question and so much more! Thank you ! What is in the rest of the space in that enormous head? Here in Connecticut we are trying to get the black bears relocated for their safety and ours, and fighting trophy kill legislation. YOU helped.