WILTIMS #136: Eye see you

You know how at twilight, blue lights seem to have a fuzzy halo (or a fuzzier halo than the other colors (you should get your eyes checked))?

TIL: ...why blue lights always look so blurry! It's a combination of chromatic aberration and our evolutionary attempt to control that aberration. Think of a prism, spreading white light into a rainbow. It does this because light of different colors is deflected differently as it transitions between two substances (with different refractive indexes).

The human eye has two kinds of light receptors, rods and cones. Rods are responsible for seeing in the dark and providing peripheral vision. They only detect one wavelength so we can only see in black in white in very dark environments. The nice thing about rods is that they are found all over the retina, so you have a full wide-angle view.

Cones, on the other hand, only work well in brighter light and come in 3^* flavors: red, green and blue. The problem with this is chromatic aberration. The image coming into your eye is bent by the cornea, lens, and various fluids. The three wavelengths separate from each other and project three slightly offset images on the retina. You can see absorbance curves for rods and cones above. Can you tell which one is the odd color out? Blue! When your eye focuses light on the retina, it does the best it can to minimize the aberration, so it focuses somewhere between the focal points of the red and green cones and just ignores blue.

So why don't you see blurry blue things all the time? To attempt to counteract its shoddy focussing, the retina messes with the distribution of the different color detecting cones. Whereas rods are all over the place, cones are almost entirely in the center of the eye, called the fovea. But blue cones are both less prevalent throughout the retina and not present at all in the center of the fovea. Your brain does some photoshop magic to make sure you think blue things are blue even though you don't directly see blue in the center of your vision.

So when lighting is dim and cones are strained, blue gets the shortest end of the stick. And that is why blue lights look fuzzier than other colored lights.

*There is actually a fourth human cone that can detect yellow wavelengths. It's absolutely fascinating but frustrating to talk about because we don't have words to describe what these people see. There's a great Radiolab podcast on it. Also, human eyes have nothing on the mantis shrimp.

WILTIMS #135: A busy day in the life of me

Today was a busy day. Here's the rundown:

• 3 hours of lecture
• Behavioral science on childhood development
• Lunch
• Neuroanatomy lab
• Poking brains and reading MRIs
• Pick-up soccer game
• Playing with upperclassmen and a surgeon from the medical center
• Surgery interest club
• Literature review (and free food) in the surgery lab at the hospital

Last night my apartment also hosted a late season interviewee, which was a nice reminder of how lucky we are to have made it to this stage.

TIL: Sigmund Freud never actually studied any children when coming up with his theories on child development. Take from this what you will...

Object permanence and object constancy are slightly different concepts. Permanence is the acknowledgement that objects exist even when unobserved (i.e. "Where'd the ball go?" gets much less interesting). Object permanence usually develops between 8 months and 1 year of age.* Constancy is the maintenance of a consistent mental idea of an object or person (e.g. Mom is Mom not some random lady).

* Amusingly, object permanence was debatable in my college-level intro to philosophy class. How can you be certain that all of existence doesn't disappear when you aren't sensing it?

WILTIMS #134: May the (inertial) force be with you!

TIL ...how Star Tours works! Your brain/ears can't distinguish between forward acceleration and upward tilt. So when you jump to "lightspeed," they just tilt the entire craft backward and your simple brain, expecting to go forward and not seeing anything to confirm that you

're tilting, happily goes along with the illusion.

The malleolus (hammer (or mallet) of the ear) points posteriorly (backward) when viewed from the internal auditory meatus (ear canal).

Hearing should never be asymmetric between the two ears; if it is, that is always significant.

In Waardenburg syndrome, congenital hearing loss is associated with heterochromia iridum (different colored eyes) as both are formed at a similar stage of development.

Caloric nystagmus is a useful diagnostic indicator (and apparently a fun, if wet, cocktail party trick) where you squirt water of different temperatures at each ear while laying down. This causes a convection effect (hot fluid rises) within the horizontal semicircular canal of the vestibular system. Fluid moving within the canals tells the ears that your head is turning, even though it's not, and your brain reacts by pointing your eyes the opposite direction to the perceived movement. The net result on a health person after you squirt water in their ears is that they will feel really dizzy and their eyes will move uncontrollably away from the warm water ear.

WILTIMS #133: That's not punny

Attendance in class today was as low as the number of classmates with hangovers was high. Last night was our school's spring formal and each neuroscience professor managed to crack a joke about the impaired brains of our absent colleagues.

TIL: There is an area in the brainstem (the parvocellular reticular nucleus) that controls involuntary movements of facial expression. Since this is a separate tract from voluntary movement, it makes possible some peculiar disorders. When such a person is asked to smile, they can't, but if you tell a joke, they will smile normally - assuming the joke is funny. Don't start accusing people of having brain damage just because they don't appreciate your terrible puns.

The Artery of Percheron is an anomalous formation where the diffuse arterioles that normally supply the thalamic midbrain region are consolidated into one small artery. This is dangerous because a small clot can block this vessel and cause a stroke characterized by an immediate loss of consciousness.

Nociceptor is the term for a pain receptor. The prefix comes from the Latin word for "harm," the same word found in the Hippocratic idiom Primum non nocere - "First, do no harm."

The drug naloxone is an opioid receptor antagonist that can block the placebo effect. This is of special interest because it shows that the placebo effect is not purely psychological but somewhat physiological.

WILTIMS #132: Short coats

Today was the first time we got to go on the hospital wards (psychiatric or otherwise) as medical students. Up to this point when we've donned our white coats and ties/female-nice-clothes (usually not both), patients have been brought to us. It was rather exciting and a dash frightening to be in this new environment. People tend to assume you know what you're doing if you look the part, and looking the part is just about all we are capable of at this point.

In group of about ten, we watched a psychiatric attending interview a patient. Perhaps the starkest indication of our naive inadequacy was our cursory assessment of this patient. He seemed to be doing very well and as the interview concluded we felt pretty optimistic about his prospects. The moment the he left the room, the doctor turn to us and said, "Sadly, the prognosis is not good for him." The disappointment was palpable. Ah well. There were two third years in the room who seemed far more with-it, so give it some time.

TIL: Borderline personality disorder gets its name from being in the middle of the spectrum from psychotic to neurotic disorders.

WILTIMS #131: I'm droopy... or have a cranial nerve palsy

I thought we already covered cranial nerves in gross anatomy all those months ago. I was wrong. Oh so wrong. The 2½ hours of lecture this morning exclusively on cranial nerves and their associated spinal cord nuclei taught me that the hours spent in gross anatomy were just a friendly introduction to convoluted roadmap of neurons that control an enormous amount of the head and body from a scattered core of seemingly indistinguishable spinal cord chunks. An we still have several lectures to come on eyesight and the optic nerve (CNII).

This afternoon we had a fantastic lecture on the ethics of procreation and genetic testing by this guy. He managed to quickly and objectively sum up the arguments from everything from abortion to cloning to "designer children." One of the more interesting points was on the future of certain technologies and their impact on the long held ethical beliefs of all parties involved. How does the debate over abortion change one we create the artificial uterus? That's not ridiculous to think about considering how medical science has continued to push back the limits of premature viability and push forward in vitro early embryonic development.

TIL: One of the cranial nerve exams is to have the patient sick out his or her tongue. If it deviates to the right, either the upper motor neuron of the left hypoglossal nerve (CNXII) or the right lower motor neuron has been damaged.

Along the same theme, because the upper portion of the face is innervated by both sides of cranial nerve VII but the lower muscles of facial expression are innervated purely contralaterally (from the opposite side), if you have a left upper motor neuron lesion you will have a droopy lower right face, while a lower motor neuron lesion will result in a Bell's palsy (half face droopiness) in the ipsilateral side.

If one of the abducens nerves (CNVI) is damaged, it will result in double vision that resolves if the patient turns his or her head. The troclear nerve (CNIV) also causes double vision when damaged resulting in a short of twisting of the eye within the socket. Patients can cancel out the distortion by awkwardly tilting their heads.

"Brain birth" is a concept analogous to brain death accepted by some proponents of abortion rights that states that, just as adults who have been rendered irreparably unconscious are declared legally dead before their heart and lungs have stopped working, unborn fetuses should not be considered alive until the brain had developed enough to be meaningfully useful.

WILTIMS #130: Metaphorical iceberg off the starboard bow!

Well, I survived at least one of yesterday's tests (further grades pending)! Thankfully we have no more exams until after spring break. I don't think I've ever anticipated a spring break as much as this one. I'm not going anywhere terribly interesting or planning any rowdy debauchery, but just sitting/sleeping for a while sounds amazing.

Freud's iceberg metaphor for the mind

Today in Behavioral Science we started talking about psychoanalysis, including Freud's id, ego, and superego. Amusingly, the last time I learned about Freud was in the hardest class to explain on my college transcripts: German 187: Satan in German Literature. This was taught in English, not German, and basically consisted of watching horror films and pretending like there was some connection with legitimate academic thought. Bizarre interpretations of Freud came up frequently. I somehow got upper-division writing credit for this and (to my knowledge) not one med school challenged me when I used this as one of my writing prerequisites. Good times.

TIL: While denial, distortion, and projection are considered narcissistic defenses, neurotic defenses include dissociation, displacement, repression, rationalization, isolation, and intellectualization.