9/20/2023 0 Comments Leech brains![]() Hirudo is an ideal animal for such investigations, because of its reliable responses to visual and non-visual stimuli, the simplicity and accessibility of its nervous system, and the robustness of its responses even after extreme surgery. The goal of my lab is to find out how their nervous system solves this challenge and produces a coherent decision for subsequent motion. Under more general circumstances, cues from both modalities are available, and leeches must either combine the two modalities, or decide which one is more reliable and selectively ignore the other. Remarkably, they can also find their prey using sensory stimuli alone: when placed in a shallow tank, they will swim toward a disturbance in a second tank placed above theirs but mechanically isolated from it. Leeches can find their prey in total darkness, relying on water-wave sensors on their skin. When a mammal steps into the water and splashes around, the leech will swim toward the source of the disturbance to find its prey. Hirudo is an obligate sanguivore that preferentially feeds on mammalian blood. My lab studies the neuronal basis for such ``multisensory integration'' in the medicinal leech Hirudo verbana. When individual cues are not 100% reliable, combining cues greatly aids decision making and it makes behavior more robust under variable circumstances. Most animals combine cues from multiple sensory modalities to gain information about their environments. Obtaining information from the environment to guide behavior is one of the most fundamental functions of nervous systems. In analyzing this data set, a particular focus will be on neurons and synaptic connections that span multiple behavioral circuits, to determine their roles in selecting behaviors. Combining the activity record with the reconstructed connectome based on the SBEM images will establish a data set with unprecedented potential for advancing our understanding of the link between neuronal connectivity and behavior. (See our recent eLife paper.) One of these ganglia is presently being sliced and imaged in a serial blockface electron microscope (SBEM). We have already obtained a simultaneous activity record of all the individual neurons in several ganglia as they generate several behaviors. Using electrophysiology to add functional significance to the anatomical connectome.Using electron microscopy to reconstruct the full connectivity pattern-the “connectome”-of the same ganglion that was imaged.Recording the activity of all the neurons in a ganglion-the unit of activity in this animal’s brain-using high-resolution voltage-sensitive dye imaging as the animal performs four different behaviors: swimming, crawling, local bending, and shortening. ![]() We use the relatively simple nervous system of the European medicinal leech to develop insights about how the activity of all the cells in a nervous system together produce individual behaviors from overlapping functional networks, a phenomenon that-at a much larger scale and undoubtedly with many complexities added-is also crucial to human brain function. These provide attractive stepping stones for understanding our own complex brain. Even now, the limitations mentioned no longer apply to certain less complex, more experimentally approachable brains. We stand at the cusp of a revolution in recording and imaging technology that will ultimately allow us to investigate comprehensively how the fundamental biological building blocks of the human brain are constructed and fit together. Yet, our understanding of even the simplest circuits remains spotty, in part because available technology has limited researchers to studying only one or a few aspects of a circuit at a time. There is mounting evidence that complex behaviors result from the activity of a multitude of simpler (sometimes competing) circuits. ![]() ![]() How brain activity can lead to complex and flexible behavioral outputs has fascinated neuroscientists and philosophers alike. Research Elucidating interactions between behavior-generating circuits using functional and anatomical connectomics ![]()
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