It’s pitch black as we ascend toward the faint halo outlining the ridge against the dark sky. We are like moths, though the light comes neither from the moon nor from a candle. The light is Los Angeles, and the ridge—the forefront of the San Gabriel Mountains—shelters us now from its depressing beauty. Los Angeles, a luminous malignancy on the night side of Earth.

We cover a few switchbacks, and the ridge grows a crown of antennas. Mount Wilson looms closer. Usually home of the historic observatory, tonight it’s transformed into an aid station where we’ll be able to pause and breathe again. I picture giant moths clinging to the far side of the mountain. For now, all we see are their antennae, but at any moment they could take flight, eclipsing the stars. I want to share the image with the runner I’m pacing, but instead I stumble into a linguistic discovery: in English, unlike in Polish, the word for the insect appendages is the same as the word for transmission devices.

We drop into a narrow ravine and the sky disappears. On the downhill we move faster, and suddenly I sense the space around us is textured not by light but by heat-pockets of warmth and chill arranged invisibly in the dark. I say it aloud to distract my companion from the pain of his eightieth mile: “I wonder what creates these thermal pockets.” Then I let myself spiral into hypotheses—different rocks holding heat with different inertia, vegetation releasing moisture at uneven rates, rugged terrain shaping subtle air flows. Another thought strikes me: in this darkness, with so little visual input, my brain has begun to map the terrain through temperature gradients. Until I voiced it, this heat-topography had been my working model of the space around me. I know it must diverge wildly from the actual ridges and gullies, but the moving body insists on some kind of map, so the mind supplies one. I recall birds that ride convection currents to soar higher, and I imagine their brains generating models of space from both thermal and visual cues—far more precise than mine.

The mountains and the darkness dissolve. I am standing in a vast, empty parking lot in daytime Los Angeles. It’s the usual scorching August, the heat spread evenly across the gray concrete like melted butter. Lost in recollections of the night run, I walk as Prelude No. 4 in E-flat minor by Scriabin seeps from my earbuds. Something uncanny happens: as the first bars sound, my brain synesthetically conjures a moving pocket of warmth, as if music itself had generated a spatial heat map around me. At first I take it as metaphor, a poetic costume draped over a banal experience. But no—it feels more like a sensation than a thought. I remember the San Gabriel heat-pockets and wonder if the same neural circuitry is at work, building topographies from whatever cues are available. This time, the cue is… music. I stop analyzing and just enjoy the strange ways of the mind.

I get to my car and start driving. As I sit still, the world behind the windshield unspools. Once again I marvel at the brain as a world-generator. Then I turn up the AC, because the heat-pocket I just got into is way too real.