Harley Lab

Throughout my career I have been interested in how sensory information guides motor decisions. Despite their seeming simplicity, invertebrates are capable of complex behaviors. As with higher vertebrates, behavioral complexity depends on the brain. My thesis work focused specifically on the central complex, a region of the insect brain composed of multiple sub-regions. My work showed that each of these sub-regions had its own function in governing particular complex behaviors. Ultimately, my work has helped to illuminate how encoded sensory information passes from structure to structure eventually becoming transformed into motor commands. At the cellular level, how does sensory information morph into motor commands? This question led me to study the leech-- a system which has been used to identify neural circuits underlying many behaviors at the level of individual cells. Some of the best studied circuits are involved in controlling rhythmic behaviors such as swimming and crawling. Why would a leech choose one behavior over another? In my research, I found that during predatory behavior, leeches are biased toward crawling, and crawling makes them better able to localize pretty. In contrast, another study showed that when presented with UV light, a noxious stimulus, leeches swim away from its source. Armed with these robust behavioral responses and a suite of anatomical and physiological tools, I aim to examine, at the level of the neural network, how sensory information such as this is encoded and used to guide context-dependent locomotor decisions.

In my lab we have several ongoing projects. All center around examining how simple nervous systems are able to create complex behaviors. The medicinal leech has 10,000 neurons (we have one billion neurons) and they are still able to locate food, mates, and negotiate complex environments. My goal is to learn how they do these things. Specific projects are as follows:

• 1. How does the visual system guide leech behavior?

We are examining how simple visual stimuli influence leech locomotion at the behavioral level. Many animals, from drosophila to humans, have a simple reflex called an optimotor response where they orient toward moving bars. We are trying to determine if this response is present in leeches. There are several theories behind the neural control of this response however their validity cannot be tested on current model systems due to the intrinsic complexity of those systems. If the leech has this response, we could determine how their neurons process this information-- something which could determine which of the current theories is most valid. This work has been presented in poster form.

Leeches have 294 eyes (10 complex and 284 simple), due to technical limitations, no one has ever examined the connections between the complex eyes and cells within the brain. This would aid us both in determining how these cells process visual information and how that response is relayed to neurons that control locomotor behavior.

2. How does physical therapy influence the recovery of a nervous system following injury?

Leeches have two ways of locomoting, they can swim and they can crawl, with the latter being the preferred behavior. When their brain is disconnected from the rest of their nervous system, they lose the ability to crawl and they swim nearly ceaselessly. My work has shown that over time, they recover the ability to crawl and the ability to stop swimming. Now we are examining if by stimulating the sensory system using physical therapy we can expedite the recovery process. How does one perform physical therapy on a leech? With a tiny treadmill outfitted with a silicone mold that challenges the leech to crawl. So far, our results are promising showing animals initiating crawl behavior many days earlier if they have had therapy. This study will enable us to determine the cellular mechanism behind how physical therapy works, something which is not known in any system.