The Ash Twins Blog

Carassius carassius, better known as the goldfish, is another fish of interest to comparative neuroanatomists. The fish has an exceptionally large vagal lobe, a brain stem structure which mediates swallowing, among other things.

Aside: the name vagal comes from the vagus nerve, which is the major input and output nerve of the vagal lobe. Vagus, which means ‘wandering’ in Latin (think vagrant), refers to the fact that the vagus nerve is the only cranial nerve [of twelve] which ‘travels’ outside the cranial cavity to mediate sensation and motility of the viscera. In fact, the vagus nerve, also known as the tenth cranial nerve, is the primary way that the brain communicates with the heart, stomach, and intestines.

Figure 1 demonstrates the vagal lobe in a partially dissected goldfish.

As you have may have noticed at some point at the pet store, goldfish eat by iteratively swallowing and spitting out big chunks of food. This feeding behavior is more subtle than it looks: goldfish are able to take in large mouthfuls of pebbles mixed with a bit of food, sort through the contents, and selectively eject the debris. This ability is mediated by the vagal lobe.

Under the microscope, the vagal lobe is quite impressive (Fig. 2a). It is comprised of 15 distinct layers (compare this to the mammalian neocortex’s 6 layers), with the 11 superficial layers mediating gustatory sensation (taste), the middle two layers allowing entry and exit of axon fibers, and the deep layers controlling contraction and relaxation of the throat (pharyngeal) muscles. The vagal lobe is a topographic map of the goldfish’s throat (pharynx) – that is, different parts of the lobe represent different parts of the throat (superficial layers sense taste in that patch of throat and deep layers control muscle tone in that patchof throat), and adjacent parts of the vagal lobe represent adjacent parts of the throat in neural tissue.

As schematized in Fig. 2b, when edible material touches one side of the goldfish’s throat, taste information from chemoreceptors on that patch of oral epithelium is communicated in the vagus nerve to the superficial layers of the vagal lobe. Superficial vagal lobe neurons integrate this information and project straight down into the deep motor layers of the same patch of vagal lobe. These projections make excitatory glutamatergic synapses onto inhibitory GABAergic interneurons in the deep layers of the vagal lobe. The inhibitory interneurons in turn inhibit the motor neurons which project back to the muscle fibers at the same patch of throat that the edible material touched. These motor neurons rhythmically drive the contraction of the throat muscles to expel debris, so when they are inhibited, the muscle lining this fraction of the throat will stay relaxed, and material in this fraction will be selectively retained.

This impressive sensorimotor reflex allows goldfish to vacuum heterogeneous debris from the lake bottom and efficiently sort the chum from the chaff. The vagal lobe’s topographic laminar architecture minimizes the wiring necessary to mediate this spatially-localized sorting function.

Second aside: Note that in mammals, the vagal lobe homologue is bifurcated into separate sensory and motor nuclei. Gustatory sensation (along with visceral sensation to the gut) is localized to the nucleus tractus solitarius, whereas motor output to the throat (and the rest of the gastrointestinal tract) is localized to the nucleus ambiguus. That these nuclei lack the intricate layering of the goldfish vagal lobe comports with their less complex and noninteracting functions.

Sources

Finger (2007) “Sorting food from stones: the vagal taste system in Goldfish,Carassius auratus”

Striedter (2008) Principles of Brain Evolution.

Matt Taibbi at Rolling Stone provides a concise history of how the investment banks became the prime beneficiaries of the government response to the financial crisis.

First, the government’s peculiar bailout of AIG precluded it from entering normal bankruptcy procedures, which would have reserved an equitable amount of AIG’s assets for all of its creditors:

As AIG headed into a tailspin that fateful summer of 2008, it looked like the beleaguered firm wasn’t going to have the money to pay off the bogus insurance. So Goldman and other banks began demanding that AIG provide them with cash collateral. In the 15 months leading up to the collapse of AIG, Goldman received $5.9 billion in collateral. Société Générale, a bank holding lots of mortgage-backed crap originally underwritten by Goldman, received $5.5 billion. These collateral demands squeezing AIG from two sides were the “Swoop and Squat” that ultimately crashed the firm. . . .

When a company like AIG is about to die, it isn’t supposed to hand over big hunks of assets to a single creditor like Goldman; it’s supposed to equitably distribute whatever assets it has left among all its creditors. Had AIG gone bankrupt, Goldman would have likely lost much of the $5.9 billion that it pocketed as collateral. “Any bankruptcy court that saw those collateral payments would have declined that transaction as a fraudulent conveyance,” says Barry Ritholtz, the author of Bailout Nation. Instead, Goldman and the other counterparties got their money out in advance — putting a torch to what was left of AIG. . . .

[A]ccording to the terms of the bailout deal struck when AIG was taken over by the state in September 2008, Goldman was paid 100 cents on the dollar on an additional $12.9 billion it was owed by AIG — again, money it almost certainly would not have seen a fraction of had AIG proceeded to a normal bankruptcy. Along with the collateral it pocketed, that’s $19 billion in pure cash that Goldman would not have “earned” without massive state intervention.

Second, the investment banks were allowed to masquerade as commercial banks, which gave them access to loans from the Federal Reserve at zero-percent interest:

Less than a week after the AIG bailout, Goldman and another investment bank, Morgan Stanley, applied for, and received, federal permission to become bank holding companies — a move that would make them eligible for much greater federal support. The stock prices of both firms were cratering, and there was talk that either or both might go the way of Lehman Brothers, another once-mighty investment bank that just a week earlier had disappeared from the face of the earth under the weight of its toxic assets. . . .

When Goldman Sachs and Morgan Stanley got their federal bank charters, they joined Bank of America, Citigroup, J.P. Morgan Chase and the other banking titans who could go to the Fed and borrow massive amounts of money at interest rates that, thanks to the aggressive rate-cutting policies of Fed chief Ben Bernanke during the crisis, soon sank to zero percent. The ability to go to the Fed and borrow big at next to no interest was what saved Goldman, Morgan Stanley and other banks from death in the fall of 2008. . . .

In fact, the Fed became not just a source of emergency borrowing that enabled Goldman and Morgan Stanley to stave off disaster — it became a source of long-term guaranteed income. Borrowing at zero percent interest, banks like Goldman now had virtually infinite ways to make money. In one of the most common maneuvers, they simply took the money they borrowed from the government at zero percent and lent it back to the government by buying Treasury bills that paid interest of three or four percent. It was basically a license to print money — no different than attaching an ATM to the side of the Federal Reserve.

“You’re borrowing at zero, putting it out there at two or three percent, with hundreds of billions of dollars — man, you can make a lot of money that way,” says the manager of one prominent hedge fund. “It’s free money.”