Cerebellar Pruning

Posted by Ashley Juavinett on October 23, 2014 in Uncategorized | Leave a comment

One day you’re chopping down an unwanted palm tree, the next you’re flashing your machete through a dense forest in god knows where. The life of a tree hacker boasted plenty of travel opportunity, but not a lot of stability. Camille swung her weapon through yet another thicket. “We better be getting bonuses for this job,” she mumbled under her breath. With a heavy swing, Jan grunted, “Seriously. I’ve never seen it this intense.”^[1]

The mission was simple: find the biggest tree and cut off all but one of the vines climbing up it. Camille and Jan thought they had hit it big – the payoff was huge, and the Greenery and Lumber Incursion Association would cover all of their expenses. The association had even bought them new, freshly sharpened machetes; now they knew why.

To make things worse, the ground rocked abruptly to and fro as they tread through the forest, as if it were balancing on the back of a turtle. It was enough to make an inexperienced and lanky tree hacker like Jan lose control of his blade.[2]

“Watch it!” Camille instructed, noticing Jan’s machete nearing a rather large hanging vine. Cutting anything but small shrubs and their target vine could cause major issues. Camille steadied her stance against the rolling ground. “You can crawl if you need to, but let’s not do any more damage then necessary.”

Mid-stride, Camille’s toe hit something big and hard, and she groaned, “As if this could be more annoying!” She teased away the hairy undergrowth to find a solid, deep brown root in front of her foot.

Jan furrowed his brow. “Follow the root,” he remembered. “Isn’t that what Bergmann said?”

“Yeah, looks like this is it,” Camille agreed. Bergmann – one of the oldest employees at G.L.I.A. – gave the best advice. He was that guy that you knew held the secrets to the entire operation, even the deepest, darkest secrets of tree hacks gone wrong.[3]

Like any good pair of protagonists in an action film, Camille and Jan nodded to each other in synchrony and looked ahead to trace the root’s trajectory. The root created a snakelike ripple in the undergrowth that continued into the deep forest and ahead, where there appeared to be a clearing. “There,” Camille suggested.

Hacking and clawing through bushes tall, fat, wide, and skinny,[4] they escaped into the clearing, and could finally see more than a yard ahead of their faces. The hill wrapped around the edge of the forest, and was topped with a line of magnificent, colossal trees peering over the land.^[5]

Camille and Jan clambered up the hill, approaching the arboreal owner of their root guide. The rolling earthquakes still had not settled. Unlike the forest, which had dense undergrowth but not much of a canopy, the hilltop was strung with vines like telephone lines. ^[6] Dense, convoluted branches and leaves emanated vertically from large tree trunks, creating a strip of coverage along the hilltop. Oddly, the tree tops were flat, an elaborate sketch on the canvas of sky behind.^[7]

A deep green vine wrapped around the hefty trunk of the tree, climbing up to the branches where it wound in and around them, like a failed knitting experiment.^[8]

“There’s only one vine going up,” Jan noticed. “Maybe it’s not this one.”

Camille looked down the line of trees. Jan was right, most of them, in fact, only had one fiber climbing up the side. “It has to be here somewhere,” she insisted, “they really wanted this done.”

Strolling down the line of gargantuan trunks, they finally came upon a tree that was riddled with vines.^[9] Camille lifted her machete over her head to prepare for the final swings of their journey. With a swift, expert swing, she came across a large section of vines crawling up the tree, and they tumbled to the ground. “Your turn,” she said to Jan.

Jan followed suit, and slash-by-slash they whittled the trunk down until just one vine remained.

“That should do it,” Camille said. The ground below them settled, and gravity finally felt like it had a unitary direction.

She looked down to the pager on her hip, now buzzing. “It’s a message from headquarters,” she read, “NICE WORK, TEAM. YOU HAVE BEEN REASSIGNED TO ANOTHER JOB UP NORTH: CEREBRAL CORTEX.”

 

Editors Note

This piece is part of a new series of brain-inspired short stories that we’ll be featuring here on NeuWrite. Check out the first installment, “Cortical Columns.” We’d love to hear who you are what you thought about it – tweet us at@NeuWriteSD!

 

Footnotes

^[1] The cerebellum is the densest part of the brain. Although it is only 10% of the brain’s mass, it contains over half of the neurons. Two of the earliest explorers of the cerebellum were Camillo Golgi and Jan Evangalista Purkinje.

[2] As the cerebellum is largely responsible for muscle coordination and fine motor control, individuals with cerebellar disorders such as cerebellar ataxia often have trouble with their balance.

[3] Bermann Glia are the most prominent glia in the cortex of the cerebellum, and are responsible for the pruning of synapses during development.

[4] The granular layer of the cerebellum has a few different cell types, including granule cells and “bushy astrocytes,” which are fairly conventionally star-shaped astrocytes. (Yamada & Watanabe, 2002). As you work your way out to the Purkinje layers, you’re more likely to encounter Bergmann glia and Purkinje cells.

^[5] Like the cortex, the cerebellum has a beautifully stereotyped and well-characterized structure. Axons travel down the middle of each cerebellar fold, known as the folia, and lead to large Purkinje cells around the border. These Purkinje cells, with a giant arbor of axons, are arguably the most ornate structures in the central nervous system.

^[6] Purkinje cells are connected by parallel fibers from granule cells. These fibers stretch across the most outer layer of the cerebellum, reaching down to synapse onto the axonal arbor of the Purkinje cell (reference).

^[7] Purkinje cells are remarkably flat!

^[8] Each mature Purkinje cell is accompanied by one climbing fiber, which wraps around the cell body and synapses there, but also intermingles with the cell’s vast axonal arbor.

^[9] During development, each Purkinje cell is innervated by multiple climbing fibers. These fibers compete, and one climbing fiber ultimately wins out, while the others are pruned away (Hashimoto et al., 2009).