Biomedical subjects

John E Lewis

Publications and source records attributed to John E Lewis.

5 recordsLinked to original sources

PubMed2004

An evaluation of performance by older persons on a simulated telecommuting task.

Telecommuting work represents a strategy for managing the growing number of older people in the workforce. This study involved a simulated customer service telecommuting task that used e-mail to answer customer queries about media-related products and company policies. Participants included 27 "younger" older adults (50-65 years) and 25 "older" older adults (66-80 years). The participants performed the task for two 2-hr sessions a day over 4 consecutive days. Although both age groups showed significant improvement across sessions on many of the performance criteria, in general the improvements were more marked for the older age-group participants. However, the participants from both age groups had difficulty meeting some of the task performance requirements. These results are discussed in terms of training strategies for older workers.

Aged↗

PubMed2003

Synaptic dynamics on different time scales in a parallel fiber feedback pathway of the weakly electric fish.

Synaptic dynamics comprise a variety of interacting processes acting on a wide range of time scales. This enables a synapse to perform a large array of computations, from temporal and spatial filtering to associative learning. In this study, we describe how changing synaptic gain via long-term plasticity can act to shape the temporal filtering of a synapse through modulation of short-term plasticity. In the weakly electric fish, parallel fibers from cerebellar granule cells provide massive feedback inputs to the pyramidal neurons of the electrosensory lateral line lobe. We demonstrate a long-term synaptic enhancement (LTE) of these synapses that is biochemically similar to the presynaptic long-term potentiation expressed by parallel fibers in the mammalian cerebellum. Using a novel stimulation protocol and a simple modeling paradigm, we then quantify the changes in short-term plasticity during the induction of LTE and show that these changes can be explained by gradual changes in only one model parameter, that which is associated with the baseline probability of transmitter release. These changes lead to a shift in the spike frequency preference of the synapse, suggesting that long-term plasticity is not only involved in controlling the gain of the parallel fiber synapse, but also provides a means of controlling synaptic filtering over multiple time scales.

Action Potentials↗

PubMed2002

Citalopram treatment for impulsive aggression in children and adolescents: an open pilot study.

OBJECTIVE: To assess the short-term effect and safety of citalopram in the reduction of impulsive aggression in children and adolescents. METHOD: Twelve subjects, aged 7 to 15 years, were attending a psychiatric outpatient clinic and had a profile of impulsive aggression. Subjects were treated in an open trial with citalopram for 6 weeks after a 1-week washout period. Dosage was regulated individually over a period of 4 weeks. The starting dose was 10 mg/day followed by 10 mg increments on a weekly basis. The maximum dose was not to exceed 40 mg/day. Outcome measures included the Modified Overt Aggression Scale (MOAS), the Child Behavioral Checklist (CBCL), and the Clinical Global Impressions (CGI). RESULTS: Eleven subjects completed the study Citalopram produced clinically and statistically significant reductions on target symptoms of impulsive aggression, independent of other behavioral problems, as measured by the MOAS, the CBCL, and the CGI at doses ranging from 20 to 40 mg/day (mean = 27 mg). No major adverse reactions were associated with citalopram use. CONCLUSION: Citalopram appears to be effective and well tolerated in this sample of children and adolescents with impulsive aggression.

Adolescent↗

PubMed2002

Dynamically interacting processes underlie synaptic plasticity in a feedback pathway.

Descending feedback is a common feature of sensory systems. Characterizing synaptic plasticity in feedback inputs is essential for delineating the role of feedback in sensory processing. In this study, we demonstrate that multiple interacting processes underlie the dynamics of synaptic potentiation in one such sensory feedback pathway. We use field recording and modeling to investigate the interaction between the transient high-magnitude potentiation (200-300%) elicited during tetanic stimulation of the feedback pathway and the lower magnitude posttetanic potentiation (PTP; ~30%) that slowly decays on cessation of the tetanus. The amplitude of the observed transient potentiation is graded with stimulus frequency. In contrast, the induction of PTP has a stimulus frequency threshold between 1 and 5 Hz, and its amplitude is independent of stimulus frequency. We suggest that the threshold for PTP induction may be linked to a minimum level of sustained potentiation (MSP) during repetitive trains of stimuli. We have developed a novel model that describes the interaction between the transient plasticity observed during train stimulation and the generation of PTP. The model combines a multiplicative, facilitation-depression-type (FD) model that describes the transient plasticity, with an enzymatic network that describes the dynamics of PTP. The model links transient plasticity to PTP through an input term that reflects MSP. The stratum fibrosum-pyramidal cell (StF-PC) synapse investigated in this study is the terminus of a feedback pathway to the electrosensory lateral line lobe (ELL) of a weakly electric gymnotiform fish. Dynamic plasticity at the StF-PC synapse may contribute to the putative role of this feedback pathway as a sensory searchlight.

Action Potentials↗

PubMed2002

Dynamics of electrosensory feedback: short-term plasticity and inhibition in a parallel fiber pathway.

The dynamics of neuronal feedback pathways are generally not well understood. This is due to the complexity arising from the combined dynamics of closed-loop feedback systems and the synaptic plasticity of feedback connections. Here, we investigate the short-term synaptic dynamics underlying the parallel fiber feedback pathway to a primary electrosensory nucleus in the weakly electric fish, Apteronotus leptorhynchus. In open-loop conditions, the dynamics of this pathway arise from a monosynaptic excitatory connection and a disynaptic (feed-forward) inhibitory connection to pyramidal neurons in the electrosensory lateral line lobe (ELL). In a brain slice preparation of the ELL, we characterized the synaptic responses of pyramidal neurons to short trains of electrical stimuli delivered to the parallel fibers of the dorsal molecular layer. Stimulus trains consisted of 20 pulses, at either random intervals or constant intervals, with varying mean frequencies. With random trains, pyramidal neuron responses were well described by a single exponential function of the inter-stimulus interval-suggesting a single facilitation-like process underlies these synaptic dynamics. However, responses to periodic (constant interval) trains deviated from this simple description. Random and periodic stimulus trains delivered when the feed-forward inhibitory component of this pathway was pharmacologically blocked revealed that inhibition and depression also contribute to the observed dynamics. We formulated a simple model of the parallel fiber synaptic dynamics that provided an accurate description of our data. The model dynamics resulted from a combination of three distinct processes. Two of the processes are the classically-described synaptic facilitation and depression, and the third is a novel description of feed-forward inhibition. An analysis of this model suggests that synaptic pathways combining plasticity with feed-forward inhibition can be easily tuned to signal different types of transient stimuli and thus lead to diverse and nonintuitive filtering properties.

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