Biomedical subjects

Adam L Taylor

Publications and source records attributed to Adam L Taylor.

5 recordsLinked to original sources

PubMed2006

Structure and visualization of high-dimensional conductance spaces.

Neurons, and realistic models of neurons, typically express several different types of voltage-gated conductances. These conductances are subject to continual regulation. Therefore it is essential to understand how changes in the conductances of a neuron affect its intrinsic properties, such as burst period or delay to firing after inhibition of a particular duration and magnitude. Even in model neurons, it can be difficult to visualize how the intrinsic properties vary as a function of their underlying maximal conductances. We used a technique, called clutter-based dimension reordering (CBDR), which enabled us to visualize intrinsic properties in high-dimensional conductance spaces. We applied CBDR to a family of models with eight different types of voltage- and calcium-dependent channels. CBDR yields images that reveal structure in the underlying conductance space. CBDR can also be used to visualize the results of other types of analysis. As examples, we use CBDR to visualize the results of a connected-components analysis, and to visually evaluate the results of a separating-hyperplane (i.e., linear classifier) analysis. We believe that CBDR will be a useful tool for visualizing the conductance spaces of neuronal models in many systems.

Algorithms↗

PubMed2006

Central pattern generating neurons simultaneously express fast and slow rhythmic activities in the stomatogastric ganglion.

Neuronal firing patterns can contain different temporal information. It has long been known that the fast pyloric and the slower gastric motor patterns in the stomatogastric ganglion of decapod crustaceans interact. However, the bidirectional influences between the pyloric rhythm and the gastric mill rhythm have not been quantified in detail from preparations that spontaneously express both patterns in vitro. We found regular and stable spontaneous gastric and pyloric activity in 71% of preparations of the isolated stomatogastric nervous system of the lobster, Homarus americanus. The gastric [cycle period: 10.96 +/- 2.67 (SD) s] and pyloric (cycle period: 1.35 +/- 0.18 s) patterns showed bidirectional interactions and coordination. Gastric neuron firing showed preferred phases within the reference frame of the pyloric cycle. The relative timing and burst parameters of the pyloric neurons systematically changed within the reference frame of the gastric cycle. The gastric rhythm showed a tendency to run at cycle periods that were integer multiples of the pyloric periods, but coupling and coordination between the two rhythms were variable. We used power spectra to quantify the gastric and pyloric contributions to the firing pattern of each individual neuron. This provided us with a way to analyze the firing pattern of each gastric and pyloric neuron type individually without reference to either gastric or pyloric phase. Possible functional consequences of these network interactions for motor output are discussed.

Action Potentials↗

PubMed2005

Invertebrate central pattern generation moves along.

Central pattern generators (CPGs) are circuits that generate organized and repetitive motor patterns, such as those underlying feeding, locomotion and respiration. We summarize recent work on invertebrate CPGs which has provided new insights into how rhythmic motor patterns are produced and how they are controlled by higher-order command and modulatory interneurons.

Animals↗

PubMed2003

Imaging reveals synaptic targets of a swim-terminating neuron in the leech CNS.

In the leech, the command-like neuron called cell Tr2 is known to stop swimming, but the connections from cell Tr2 to the swim central pattern generator have not been identified. We used fluorescence resonance energy transfer voltage-sensitive dyes to identify three neurons that are synaptic targets of cell Tr2. We then used electrophysiological techniques to show that these connections are monosynaptic, chemical, and excitatory. Two of the novel targets, cell 256 and cell 54, terminate swimming when stimulated. These neurons are likely to mediate swim cessation caused by cell Tr2 activity, and thus play the role of intermediate control cells in the leech CNS.

Animals↗

PubMed2002

Analysis of oscillations in a reciprocally inhibitory network with synaptic depression.

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 which stable oscillations occur, as well as the period and amplitude of these oscillations. These expressions are functions of three parameters: the time constant of depression, the synaptic strengths, and the amount of tonic excitation the cells receive. We compare our analytical results with the output of numerical simulations and obtain good agreement between the two. Based on our analysis, we conclude that the oscillations in our network are qualitatively different from those in networks that oscillate due to postinhibitory rebound, spike-frequency adaptation, or other intrinsic (rather than synaptic) adaptational mechanisms. In particular, our network can oscillate only via the synaptic escape mode of Skinner, Kopell, and Marder (1994).

Animals↗