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Decision making can be a complex task involving a sequence of subdecisions. For example, we decide to pursue a goal (e.g., get something to eat), then decide how to accomplish that goal (e.g., go to a restaurant), and then make a sequence of more specific plans (e.g., which restaurant to go to, how to get there, what to order, etc.). In characterizing the(More)
Dendritic processing of glutamatergic synaptic inputs was investigated in the anterior pagoda cell of leech. We observed that below spike threshold, the amplitude of individual EPSPs decreased with hyperpolarization and that simultaneous stimulation of pairs of synaptic inputs leads to the supralinear summation of EPSPs. Voltage-clamp measurements revealed(More)
We investigated decision-making in the leech nervous system by stimulating identical sensory inputs that sometimes elicit crawling and other times swimming. Neuronal populations were monitored with voltage-sensitive dyes after each stimulus. By quantifying the discrimination time of each neuron, we found single neurons that discriminate before the two(More)
In the leech Hirudo medicinalis inhibitory motor neurons to longitudinal muscles make central inhibitory connections with excitatory motor neurons to the same muscles. We have used a variety of physiological and morphological methods to characterize these inhibitory connections. The efficacy of the transmission between the inhibitors and the excitors was(More)
The present study examines the morphological development of a highly organized muscle layer in the leech Hirudo medicinalis, in an effort to characterize those factors that are important in directing its assembly. The tubular body wall of the leech contains 3 major muscle layers that are anatomically distinct: an inner layer of longitudinal muscle, an outer(More)
Leeches swim by undulating their extended and flattened body in the dorsoventral direction, to form a wave that travels backwards along the animal. The troughs and crests of this body wave are produced by a metachronal rhythm of antiphasic contractions of the dorsal and ventral longitudinal musculature of the body wall of successive segments.(More)
We present and analyze a model of a two-cell reciprocally inhibitory network that oscillates. The principal mechanism of oscillation is short-term synaptic depression. Using a simple model of depression and analyzing the system in certain limits, we can derive analytical expressions for various features of the oscillation, including the parameter regime in(More)
To form accurate representations of the world, sensory systems must accurately encode stimuli in the spike trains of populations of neurons. The nature of such neuronal population codes is beginning to be understood. We characterize the entire sensory system underlying a simple withdrawal reflex in the leech, a bend directed away from the site of a light(More)
The ability of distinct anatomical circuits to generate multiple behavioral patterns is widespread among vertebrate and invertebrate species. These multifunctional neuronal circuits are the result of multistable neural dynamics and modular organization. The evidence suggests multifunctional circuits can be classified by distinct architectures, yet the(More)
Central pattern generators (CPGs) control both swimming and crawling in the medicinal leech. To investigate whether the neurons comprising these two CPGs are dedicated or multifunctional, we used voltage-sensitive dye imaging to record from approximately 80% of the approximately 400 neurons in a segmental ganglion. By eliciting swimming and crawling in the(More)