Due to its sophisticated genetics, relatively simple anatomy, rich array of behaviors, and its remarkable conservation of molecular mechanisms to mammals, Drosophila has become the ”°Jack of all trades”± in the life sciences. The current research interest of our lab is to understand the molecular, cellular, and integrative mechanisms underlying learning, memory and higher cognitive functions, e.g., decision-making and cross-modal memory synergism, in Drosophila. In particular, we aim at understanding how neural circuit might use the reward information for controlling goal-directed behavior, such as selective attention, decision-choice-action and intentional behavior.
In addition to the main line of research described above, we have also pursued several side-projects, including thermal nociception, circadian clock, male-male courtship, drug addiction as well as the neurodegenerations in flies. The long-term goal in these projects is elucidate whether the circuits underlying addictive or courtship behaviors have anything in common with those required for decision making processes.
1. Non-Fourier Motion Perception
There are two motion perception systems in the human visual system: the first-order system that uses a primitive motion energy computation to extract motion from moving luminance modulations, and the second-order system that uses motion energy to extract motion from moving texture-contrast modulations. The second-order motion has three forms: contrast, flicker and texture. Recently, a third-order system that tracks features including depth-modulated motion, isoluminant chromatic motion, and motion-modulated motion has been proposed. As in humans, we found first-order (luminance-defined or Fourier) signals for a tethered fly in the flight simulator is important to motion perception. Interestingly, Non-Fourier (including second-order and third-order) signals are also detectable in Drosophila in the absence of first-order signals.
2. Experience-dependent visual feature extraction
Visual feature extraction is defined as the selection of the main component of a system from multiple visual features, such as color, shape, etc. Fruit flies are able to learn both color and shape features. We found that flies showed improved ability of feature extraction following prior experience. However, flies lacking the mushroom body could not use prior experience to help choose the correct feature even after learning this feature. Our results indicate that prior experience enhanced visual feature exaction in Drosophila and that the mushroom body is required in this process.
3£®Mushroom bodies (MBs) improve contrast discrimination
Attention is the cognitive mechanism by which salient or behaviorally relevant sensory information is selected for perception and awareness. At any given time, only a small amount of visual information on the retina can be processed and used further in the control of behavior. We found that MBs mediate attention-like behavior in visual object tracking paradigms in the flight simulator. MBs can substantially increase visual contrast gain at a lower contrast range and inhibit both visual and olfactory background noise in visual object tracking.
4. Novel stimulus-induced calcium efflux in Drosophila's Mushroom bodies
The physiological properties of MBs neurons remain elusive. Using calcium-imaging technique we found that electrical stimulation dramatically induced a reduction of calcium level, instead of calcium level increase, in the termini of the MB fibers. This novel calcium decrease is mainly specific to some parts of MBs neurons. The block of GABA receptors promoted calcium propagation through the MB fibers, but did not disrupt electrical stimulation-induced calcium level decrease. Our findings indicated that sodium-calcium exchangers play an essential role in regulating calcium efflux in Drosophila's MBs.