Search PubMed⌕ Search

Biomedical subjects

John K Chapin

Publications and source records attributed to John K Chapin.

9 recordsLinked to original sources
PubMed2007

The reach-to-grasp-food task for rats: a rare case of modularity in animal behavior?

Humans and non-human animals make use of sensory hierarchies in "selecting" strategies for solving many cognitive and behavioral tasks. Often, if a preferred type of sensory information is unavailable or is not useful for solving a given task, the animal can switch to a lower-priority strategy, making use of a different class of sensory information. In the case of rats performing a classic reach-to-grasp-food task, however, prior studies indicate that the reaching maneuver may be a fixed action pattern that is guided exclusively by the food's odor plume until the point of contact with the food morsel [Whishaw IQ, Tomie JA. Olfaction directs skilled forelimb reaching in the rat. Behav Brain Res 1989;32(1):11-21; Metz GA, Whishaw IQ. Skilled reaching an action pattern: stability in rat (Rattus norvegicus) grasping movements as a function of changing food pellet size. Behav Brain Res 2000;116(2):111-22; Whishaw IQ. Did a change in sensory control of skilled movements stimulate the evolution of the primate frontal cortex? Behav Brain Res 2003;146(1/2):31-41]. We sought to confirm and extend these findings in several ways. In Experiment 1, using a GO/NO-GO variant of the classic task, we demonstrated that rats used the GO target's odor both to trigger and guide their reaches. In Experiment 2, we showed that rats deprived of (a) vision, (b) object-recognizing rostral whiskers and forearm sinus hairs, or (c) both, displayed no deficits in triggering and guiding their reaches. Finally, in a third experiment in which the GO target's location varied randomly across trials and only olfactory cues were available, we demonstrated that rats could determine the spatial endpoint of their reach without any loss of accuracy. Combined with results from a prior study in which bulbectomized rats never developed a new, successful reaching strategy despite extensive post-operative training [Whishaw IQ, Tomie JA. Olfaction directs skilled forelimb reaching in the rat. Behav Brain Res 1989;32(1):11-21], these results indicate that rats do not have a sensory hierarchy for solving the reach-to-grasp-food task, but rather, are guided by olfaction alone until their paw contacts the food morsel.

Animals↗
PubMed2006

Neural ensemble activity from multiple brain regions predicts kinematic and dynamic variables in a multiple force field reaching task.

In everyday life, we reach, grasp, and manipulate a variety of different objects all with their own dynamic properties. This degree of adaptability is essential for a brain-controlled prosthetic arm to work in the real world. In this study, rats were trained to make reaching movements while holding a torque manipulandum working against two distinct loads. Neural recordings obtained from arrays of 32 microelectrodes spanning the motor cortex were used to predict several movement related variables. In this paper, we demonstrate that a simple linear regression model can translate neural activity into endpoint position of a robotic manipulandum even while the animal controlling it works against different loads. A second regression model can predict, with 100% accuracy, which of the two loads is being manipulated by the animal. Finally, a third model predicts the work needed to move the manipulandum endpoint. This prediction is significantly better than that for position. In each case, the regression model uses a single set of weights. Thus, the neural ensemble is capable of providing the information necessary to compensate for at least two distinct load conditions.

Algorithms↗
PubMed2005

Rapid learning and flexible memory in "habit" tasks in rats trained with brain stimulation reward.

Two groups of rats, one rewarded with sweetened food and the other rewarded with medial forebrain bundle (MFB) stimulation, were trained to home in on and dig for a buried object coated with a target odor. After each group had 15 training trials, MFB rats searched with greater accuracy and speed than food-rewarded rats. MFB rats were subsequently tested (1) after 6 weeks with no additional practice; (2) with food or non-food distractor odors, and (3) with major spatial alterations to the search environment, and in all cases searched with the same high accuracy, short search time, and low level of distractibility as in baseline. These results suggest that the high motivation provided by MFB reward engenders rapidly formed, long-lasting, and surprisingly flexibly deployable "habit" memories.

Animals↗
PubMed2004

A multi-channel telemetry system for brain microstimulation in freely roaming animals.

A system is described that enables an experimenter to remotely deliver electrical pulse train stimuli to multiple different locations in the brains of freely moving rats. The system consists of two separate components: a transmitter base station that is controlled by a PC operator, and a receiver-microprocessor integrated pack worn on the back of the animals and which connects to suitably implanted brain locations. The backpack is small and light so that small animal subjects can easily carry it. Under remote command from the PC the backpack can be configured to provide biphasic pulse trains of arbitrarily specified parameters. A feature of the system is that it generates precise brain-stimulation behavioral effects using the direct constant-voltage TTL output of the backpack microprocessor. The system performs with high fidelity even in complex environments over a distance of about 300 m. Rat self-stimulation tests showed that this system produced the same behavioral responses as a conventional constant-current stimulator. This system enables a variety of multi-channel brain stimulation experiments in freely moving animals. We have employed it to develop a new animal behavior model ("virtual" conditioning) for the neurophysiological study of spatial learning, in which a rat can be accurately guided to navigate various terrains.

Animals↗
PubMed2004

Using multi-neuron population recordings for neural prosthetics.

Classical single-neuron recording methods led to 'neuron-centric' concepts of neural coding, whereas more recent multi-neuron population recordings have inspired 'population-centric' concepts of distributed processing in neural systems. Because most neocortical neurons code information coarsely, sensory or motor processing tends to be widely distributed across neuronal populations. Dynamic fluctuations in neural population functions thus involve subtle changes in the overall pattern of neural activity. Mathematical analysis of neural population codes allows extraction of 'motor signals' from neuronal population recordings in the motor cortices, which can then be used in real-time to directly control movement of a robot arm. This technique holds promise for the development of neurally controlled prosthetic devices and provides insights into how information is distributed across several brain regions.

Action Potentials↗
PubMed2004

Ceramic-based multisite electrode arrays for chronic single-neuron recording.

A method is described for the manufacture of a microelectrode array for chronic, multichannel, single neuron recording. The ceramic-based, multisite electrode array has four recording sites patterned onto a ceramic shaft the size of a single typical microwire electrode. The sites and connecting wires are applied to the ceramic substrate using a reverse photolithographic procedure. Recording sites (22 x 80 microm) are separated by 200 microm along the shaft. A layer of alumina insulation is applied over the whole array (exclusive of recording sites) by ion-beam assisted deposition. These arrays were capable of recording single neuron activity from each of their recording sites for at least three weeks during chronic implantation in the somatosensory cortex of rats, and several sites had recordings that lasted for more than 8 weeks. The vertical arrangement of the recording sites on these electrodes is ideal for simultaneously recording across the different layers of brain areas such as the cerebral cortex and hippocampus in chronic preparations.

Action Potentials↗
PubMed2004

Force field apparatus for investigating movement control in small animals.

As part of our overall effort to build a closed loop brain-machine interface (BMI), we have developed a simple, low weight, and low inertial torque manipulandum that is ideal for use in motor system investigations with small animals such as rats. It is inexpensive and small but emulates features of large and very expensive systems currently used in monkey and human research. Our device consists of a small programmable torque-motor system that is attached to a manipulandum. Rats are trained to grasp this manipulandum and move it to one or more targets against programmed force field perturbations. Here we report several paradigms that may be used with this device and results from rat's making reaching movements in a variety of force fields. These and other available experimental manipulations allow one to experimentally separate several key variables that are critical for understanding and ultimately emulating the feedforward and feedback mechanisms of motor control.

Animals↗