HEIDE, G. (1983). Neural mechanisms of flight control in Diptera. In Insect Flight II (ed. W. Nachtigall), Biona Report 2, pp. 35–52. Stuttgart: G. Fischer.
The Holidays are a great time to kick back and read some old obscure review articles. So here is a recommendation from the jolly folks at Sick Papes: Gerhard Heide’s leisurely tour through all the badass experiments he did in the 60’s and 70’s while our dads were busy drinking Schlitz and grooving to the Allman Brothers.
(A word of warning before we get started: this pape is completely impossible to find unless you live with and regularly sex up a science librarian: I suggest you plan ahead by picking one of your elementary school classmates and spend 20 years cultivating him/her into the world’s premier source of obscure biology papes.)
Like many Germans during the sexual revolution, Gerhard Heide wanted to understand how flying insects control their wings as they cruise through the air. For decades, biomachinists had been measuring the forces and movements of fly wings. In separate quarters, electrophysiologists had recorded from the neurons and muscles that produced these movements. What Heide set out to do was merge these two pursuits- record from the flight motoneurons and muscles while the animal was flying. Heide’s pape describes two decades of incredible detailed work. I’ll summarize a mere morsel here to whet your Holiday appetite.
Flies have two types of flight muscle: the indirect flight muscles and the steering muscles. The indirect flight muscles provide the power for each wingstroke. These power muscles are asynchronous muscles—they fire only a single action potential per 40-50 wingbeats. This is necessary because flies beat their wings very fast (up to 250 times a second), and it would be difficult for a muscle to keep up at that rate. Heide was the first to show, in the early 1970’s, that there is no fixed relationship between the spike timing of the indirect flight muscles and the wingbeat.
However, flies require not only power to fly straight; they also need to be able to gracefully maneuver around obstacles. This is accomplished by the steering muscles, which exert smaller forces on the wing hinge to tweak the shape and timing of the wingstroke. Steering muscles are synchronous—their spike rate directly controls the rate of muscle contraction. And because they must modulate individual wingbeats, the timing of their action potentials must fall precisely within a particular phase of the wingstroke. What, Heide asked, ensures this timing?
To answer this question, our man ablated different parts of the wing and haltere nerves and recorded simultaneously from the indirect flight muscles and the steering muscles, while measuring the precise position of the wings during flight. He found that ablating the wing and haltere nerves disrupted phase-locked spiking of steering muscles, suggesting that afferent input to the steering muscles enforces steering muscle timing. In other words, the fly does not have a clock (or central pattern generator) that controls both the steering and power muscles. Rather, there is some sensor on the fly that detects each wingstroke and sets the phase of the steering muscles. Later experiments by one of Heide’s disciples showed that afferent input from both haltere and wing mechanoreceptors structure the firing patterns of specific steering muscles.
In addition to the story I just synopsized, this pape contains all sorts of crazy unpublished experiments and anecdotal claims. In one case, Heide and a couple other heroes (Foster and McCann) recorded from two steering muscles and the infamous motion-sensitive H1 neuron during flight. People don’t write reviews like this anymore. And for good reason- solid conclusions should not be based on solitary examples and subjective descriptions. However, the sketch of a sunglass-wearing Heide on the cover page of this pape is enough to convince me that a single experiment from Gerhard Heide’s hands is more valuable than a million replicates from an army of goddamn amateurs.