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Scott L Hooper

Publications and source records attributed to Scott L Hooper.

15 recordsLinked to original sources
PubMed2006

Natural neural output that produces highly variable locomotory movements.

We recorded fast extensor tibiae motor neuron activity during single-legged treadmill walking in the stick insect, Carausius morosus. We used this activity to stimulate the extensor muscle motor nerve, observed the resulting extensor muscle contractions under isotonic conditions, and quantified these contractions with a variety of measures. Extensor contractions induced in this manner were highly variable, with contraction measures having SDs of 12 to 51%, and ranges of 82 to 275%, when expressed as percentages of the means, an unexpectedly wide range for a locomotory pattern. Searches for correlations among the contraction measures showed that, in general, this high variability is not reduced by contraction measure covariation. Comparing responses (to identical input) across animals showed that extensor muscles from different animals generally significantly differed from one another. However, correlation analyses on these data suggested that these differences do not indicate that multiple extensor muscle subtypes exist. Extensor muscles instead appear to belong to a single class, albeit one with high animal to animal variability. These data thus provide another well-quantified example (along with Aplysia feeding) of a repetitive but highly variable motor pattern (in contrast to the high rhythmicity and stereotypy present in most other well-quantified repetitive motor patterns). We suggest this high variability could be an adaptive combination of locomotion, active sensing, and crypsis arising from the relatively low demand for locomotion in Carausius behavior, the highly fragmented environment the animal inhabits, and its need to avoid predatory attention.

Action Potentials↗
PubMed2006

Motor control: the importance of stiffness.

An octopus brings food grasped by a tentacle to its mouth by bending the tentacle around a joint formed by stiffened distal and proximal tentacle muscles, and thus may use motor control strategies analogous to those in animals with articulated limbs.

Animals↗
PubMed2005

Movement control: dedicated or distributed?

Neural networks in which 'commands' spread 'horizontally' across multiple neurons have been believed to mediate motor pattern variation. A recent study shows that dedicated 'vertical' neural pathways can also underlie these variations.

Animals↗
PubMed2005

Invertebrate muscles: muscle specific genes and proteins.

This is the first of a projected series of canonic reviews covering all invertebrate muscle literature prior to 2005 and covers muscle genes and proteins except those involved in excitation-contraction coupling (e.g., the ryanodine receptor) and those forming ligand- and voltage-dependent channels. Two themes are of primary importance. The first is the evolutionary antiquity of muscle proteins. Actin, myosin, and tropomyosin (at least, the presence of other muscle proteins in these organisms has not been examined) exist in muscle-like cells in Radiata, and almost all muscle proteins are present across Bilateria, implying that the first Bilaterian had a complete, or near-complete, complement of present-day muscle proteins. The second is the extraordinary diversity of protein isoforms and genetic mechanisms for producing them. This rich diversity suggests that studying invertebrate muscle proteins and genes can be usefully applied to resolve phylogenetic relationships and to understand protein assembly coevolution. Fully achieving these goals, however, will require examination of a much broader range of species than has been heretofore performed.

Animals↗
PubMed2004

Behavioral plasticity: modulation occurs across time.

Modulatory inputs alter neural network activity, which, for instance, helps explain why mood affects cognition. Some neurons modulate their own networks. This 'intrinsic' modulatory feedback implies that a network's history could partially determine its present activity.

Cognition↗
PubMed2003

Lobster (Panulirus interruptus) pyloric muscles express the motor patterns of three neural networks, only one of which innervates the muscles.

In several systems, including some well studied invertebrate "model" preparations, rapid, rhythmic inputs drive slow muscles. In this situation muscle contractions can summate temporally between motor neuron bursts, tonically contract, and low-pass filter broad-band input. We have investigated how the muscles innervated by each motor neuron type of the rapid, rhythmic (cycle period, approximately 1 sec) lobster pyloric network respond when driven by previously recorded in vitro pyloric network activity from intact stomatogastric nervous systems. Under these conditions the much slower gastric mill and cardiac sac networks of the stomatogastric nervous system are also active and modify pyloric activity. All of the muscles show pyloric timed phasic contractions that ride on a sustained tonic contraction; muscle activity can range from being almost completely phasic to almost completely tonic. The modifications of pyloric neuron activity induced by gastric mill (cycle period, approximately 10 sec) activity result in some pyloric muscles showing prominent, gastric mill-timed, changes in either phasic or tonic contraction amplitude. The strong modification of pyloric neuron activity induced by cardiac sac (cycle period, approximately 60 sec) activity alters the contractions of all pyloric muscles. These changes are sufficient that for some muscles, in some preparations, the primary muscle output is cardiac sac-timed. This is the first work to examine the motor responses of all pyloric muscle classes to spontaneous stomatogastric activity and shows that the pyloric motor pattern is a complex combination of the activities of three neural networks, although only one (the pyloric) innervates the muscles.

Animals↗
PubMed2003

Relating network synaptic connectivity and network activity in the lobster (Panulirus interruptus) pyloric network.

The lobster pyloric network has a densely interconnected synaptic connectivity pattern, and the role individual synapses play in generating network activity is consequently difficult to discern. We examined this issue by quantifying the effect on pyloric network phasing and spiking activity of removing the Lateral Pyloric (LP) and Ventricular Dilator (VD) neurons, which synapse onto almost all pyloric neurons. A confounding factor in this work is that LP and VD neuron removal alters pyloric cycle period. To determine the effects of LP and VD neuron removal on pyloric activity independent of these period alterations, we altered network period by current injection into a pyloric pacemaker neuron, hyperpolarized the LP or VD neuron to functionally remove each from the network, and plotted various measures of pyloric neuron activity against period with and without the LP or VD neuron. In normal physiological saline, in many (or most) cases removing either neuron had surprisingly little effect on the activity of its postsynaptic partners, which suggests that under these conditions these neurons play a relatively small role in determining pyloric activity. In the cases in which removal did alter postsynaptic activity, the effects were inconsistent across preparations, which suggests that either despite producing very similar neural outputs, pyloric networks from different animals have different cellular and synaptic properties, or some synapses contribute to network activity only under certain modulatory conditions, and the "baseline" level of modulatory influence the network receives from higher centers varies from animal to animal.

Action Potentials↗
PubMed2003

Quantification of cardiac sac network effects on a movement-related parameter of pyloric network output in the lobster.

Cardiac sac network activity (cycle period tens of seconds to minutes) has long been known to alter pyloric network activity (cycle period approximately 1 s), but these effects have not been quantified. Some pyloric muscles extract cardiac sac timed variations in pyloric motor neuron firing, and consequently produce cardiac sac timed movements even though no cardiac sac neurons innervate them. Determining pyloric behavior therefore requires detailed description of cardiac sac effects on pyloric neural output. Pyloric muscle activity correlates well with motor neuron overall spike frequency (OSF, number of spikes per burst divided by cycle period). We therefore quantified the effects of cardiac sac activity on the OSF of all pyloric neurons in the lobster, Panulirus interruptus. The ventricular dilator (VD) neuron had a biphasic response, with its OSF first increasing and then decreasing during cardiac sac bursts. Lateral pyloric (LP) neuron OSF decreased during cardiac sac activity. The pyloric (PY) neurons had two responses, with OSF either decreasing or increasing just after the beginning of cardiac sac activity. The pyloric dilator (PD) neurons had a triphasic response, with OSF increasing slightly at the beginning of cardiac sac activity, decreasing during the cardiac sac burst, and strongly increasing after cardiac sac activity ended. The inferior cardiac (IC) neuron had a biphasic response, with OSF decreasing at the beginning of cardiac sac activity and strongly increasing when cardiac sac activity ceased. These data provide the quantitative description of cardiac sac effects on pyloric activity necessary to predict pyloric movement from pyloric neural output.

Animals↗
PubMed2002

Follower neurons in lobster (Panulirus interruptus) pyloric network regulate pacemaker period in complementary ways.

Distributed neural networks (ones characterized by high levels of interconnectivity among network neurons) are not well understood. Increased insight into these systems can be obtained by perturbing network activity so as to study the functions of specific neurons not only in the network's "baseline" activity but across a range of network activities. We applied this technique to study cycle period control in the rhythmic pyloric network of the lobster, Panulirus interruptus. Pyloric rhythmicity is driven by an endogenous oscillator, the Anterior Burster (AB) neuron. Two network neurons feed back onto the pacemaker, the Lateral Pyloric (LP) neuron by inhibition and the Ventricular Dilator (VD) neuron by electrical coupling. LP and VD neuron effects on pyloric cycle period can be studied across a range of periods by altering period by injecting current into the AB neuron and functionally removing (by hyperpolarization) the LP and VD neurons from the network at each period. Within a range of pacemaker periods, the LP and VD neurons regulate period in complementary ways. LP neuron removal speeds the network and VD neuron removal slows it. Outside this range, network activity is disrupted because the LP neuron cannot follow slow periods, and the VD neuron cannot follow fast periods. These neurons thus also limit, in complementary ways, normal pyloric activity to a certain period range. These data show that follower neurons in pacemaker networks can play central roles in controlling pacemaker period and suggest that in some cases specific functions can be assigned to individual network neurons.

Animals↗
PubMed2002

Combinatorial and cross-fiber averaging transform muscle electrical responses with a large stochastic component into deterministic contractions.

Pyloric muscles of the stomatogastric neuromuscular system of the lobster Panulirus interruptus produce highly deterministic (range, less than +/- 6% of mean amplitude) contractions in response to motor nerve stimulation with unchanging spike bursts containing physiological (5-10) spike numbers. Intracellular recordings of extrajunctional potentials (EJPs) evoked in these muscles by motor nerve stimulation revealed a large, apparently stochastic amplitude variation (range, +/- 36% of mean amplitude). These observations raised the question of how do electrical responses with a large amplitude variation give rise to deterministic muscle output? We show here that this question is likely resolved by (1) combinatorial averaging within individual muscle fibers of the multiple EJPs that occur in motor neuron bursts, and (2) averaging across muscle fibers whose electrical responses are uncorrelated. Synapses with high inherent variability are also present in vertebrate CNSs. Combinatorial averaging in multispike inputs would also reduce variation in postsynaptic response at these synapses. The data reported here provide further support that bursting presynaptic activity could make such synapses functionally deterministic as well.

Action Potentials↗
PubMed2002

A computational role for slow conductances: single-neuron models that measure duration.

Humans effortlessly interpret speech and music, whose patterns can contain sound durations up to thousands of milliseconds. How nervous systems measure such long durations is unclear. We show here that model neurons containing physiological slow conductances are 'naturally' sensitive to duration, replicate known duration-sensitive neurons and can be 'tuned' to respond to a wide range of specific durations. In addition, these models reproduce several other properties of duration-sensitive neurons not selected for in model construction. These data, and the widespread presence of slow conductances in nervous systems, suggest that slow conductances might play a major role in duration measurement.

Electric Conductivity↗
PubMed2002

Quantification of gastric mill network effects on a movement related parameter of pyloric network output in the lobster.

It has long been known that gastric mill network activity (cycle period 5-10 s) alters pyloric network output (cycle period approximately 1 s), but these effects have not been quantified. Many pyloric muscles extract gastric mill timed variations in pyloric motor neuron firing, and consequently produce gastric mill timed movements even though no gastric mill neurons innervate them. Determining pyloric behavior therefore requires detailed description of gastric mill effects on pyloric neural output. Pyloric muscle activity correlates well with motor neuron overall spike frequency (OSF, burst spike number divided by cycle period). We quantified OSF variation of all pyloric neurons as a function of time into the gastric mill cycle [as measured from the beginning of Gastric Mill (GM) neuron bursts] in the lobster, Panulirus interruptus. No repeating pattern within individual gastric mill cycles of Lateral Pyloric (LP) and Ventricular Dilator (VD) neuron OSF was visually apparent. Averaged data showed that VD and LP neuron OSF decreased (approximately 0.5 and 1.5 Hz, respectively) at the beginning of each gastric mill cycle. Visually apparent patterns of OSF waxing and waning within each gastric mill cycle were present for the Inferior Cardiac (IC), Pyloric Dilator (PD), and Pyloric (PY) neurons. However, when averaged as a function of phase or delay in the gastric mill cycle, the average changes were smaller than those in individual gastric mill cycles because when the OSF variations occurred varied considerably in different gastric mill cycles. We therefore used a "pattern-based" analysis in which an identifying characteristic of each neuron's repeating OSF variation pattern was defined as pattern pyloric cycle zero. The pyloric cycles in each repetition of the OSF variation pattern were numbered relative to the zero cycle, and averaged to create an average OSF variation profile. The zero cycle delays relative to GM neuron burst beginning were then averaged to determine when in the gastric mill cycle the profile occurred. This technique preserved the full extent of pyloric neuron OSF changes. Maximum PY neuron OSF occurred within the GM neuron burst, whereas maximum IC and PD neuron OSF occurred during the GM neuron interburst interval. Despite these changes, pyloric cycling did not phase lock with gastric mill activity, nor were an integer number of pyloric cycles present in each gastric mill cycle. In addition to providing data necessary to predict pyloric movement, this work shows how pattern-based analysis can successfully quantify interactions between nonphase-locked networks.

Action Potentials↗
PubMedDate not supplied

Crustacean motor pattern generator networks.

Crustacean motor pattern-generating networks have played central roles in understanding the cellular and network bases of rhythmic motor patterns for over half a century. We review here the four best investigated of these systems: the stomatogastric, ventilatory, cardiac, and swimmeret systems. Generally applicable observations arising from this work include (1) neurons with active, endogenous cell properties (endogenous bursting, postinhibitory rebound, plateau potentials), (2) nonhierarchical (distributed) network synaptic connectivity patterns characterized by high levels of inter-neuronal connections, (3) nonspiking neurons and graded transmitter release, (4) multiple modulatory inputs, (5) networks that produce multiple patterns and have flexible boundaries, and (6) peripheral properties (proprioceptive feedback loops, low-frequency muscle filtering) playing an important role in motor pattern generation or expression.

Action Potentials↗