Biomedical subjects

John E Lewis

Publications and source records attributed to John E Lewis.

8 recordsLinked to original sources

PubMed2006

The role of family functioning in the stress process of dementia caregivers: a structural family framework.

PURPOSE: The purpose of the study was to evaluate the role of family functioning in the stress process in a sample of caregivers of dementia patients by using a structural family framework. The stress-process model of caregiver distress included family functioning as an intervening variable in the relationship between objective burden and distress. We theorized family functioning to partially mediate the relationship between objective burden and distress and to significantly account for the prediction of distress beyond well-recognized predictors. DESIGN AND METHODS: One hundred eighty-one family caregivers from the Miami site of the Resources for Enhancing Alzheimer's Caregiver Health project participated in this study. We assessed sociodemographics, burden, depression, anxiety, and perceived health for each caregiver. We measured family functioning by using a multidimensional and observational instrument. We used structural equation modeling to assess the fit of the model for the overall sample and for different caregiver subgroups and to examine whether demographic variables affected the relationships in the model. RESULTS: The results of the study indicated that family functioning significantly contributed to distress in the overall sample and partially mediated the relationship between objective burden and distress. We also found that the stress-process model was adequately fit by the hypothesized relationships between objective burden, family functioning, and distress for the overall sample and all of the subsamples, except for wives. IMPLICATIONS: This study provides support for the structural family approach as an explanatory model for the influence of family functioning on dementia caregivers. Family structural functioning is one contributor to the caregiver stress process. This suggests that interventions targeting structural family problems may reduce caregiver distress.

Aged↗

PubMed2006

Modeling the electric field of weakly electric fish.

Weakly electric fish characterize the environment in which they live by sensing distortions in their self-generated electric field. These distortions result in electric images forming across their skin. In order to better understand electric field generation and image formation in one particular species of electric fish, Apteronotus leptorhynchus, we have developed three different numerical models of a two-dimensional cross-section of the fish's body and its surroundings. One of these models mimics the real contour of the fish; two other geometrically simple models allow for an independent study of the effects of the fish's body geometry and conductivity on electric field and image formation. Using these models, we show that the fish's tapered body shape is mainly responsible for the smooth, uniform field in the rostral region, where most electroreceptors are located. The fish's narrowing body geometry is also responsible for the relatively large electric potential in the caudal region. Numerical tests also confirm the previous hypothesis that the electric fish body acts approximately like an ideal voltage divider; this is true especially for the tail region. Next, we calculate electric images produced by simple objects and find they vary according to the current density profile assigned to the fish's electric organ. This explains some of the qualitative differences previously reported for different modeling approaches. The variation of the electric image's shape as a function of different object locations is explained in terms of the fish's geometrical and electrical parameters. Lastly, we discuss novel cues for determining an object's rostro-caudal location and lateral distance using these electric images.

Animals↗

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.

Animals↗

PubMedDate not supplied

Lidocaine 5% patch: an open-label naturalistic chronic pain treatment trial and prediction of response.

OBJECTIVE: There have been a few open-label nonplacebo reports on the successful use of lidocaine 5% patch (L5P) for other types of pain besides postherpetic neuralgia, such as chronic low back pain. With the these reports, we began to utilize L5P routinely for chronic pain patients (CPPs) with various pain diagnoses. The purpose of this report was to describe the results of a retrospective review of this open-label naturalistic L5P chronic pain treatment trial and to attempt to delineate predictors of perceived clinical response. DESIGN: Consecutive CPPs were selected for this clinical trial according to the following inclusion criteria: the CPPs with pain greater than 6-month duration and either a hyperalgesic pain area or trigger point, which could be covered by one L5P, were offered a 3-day L5P naturalistic treatment trial. The purpose of this trial was to determine which CPPs would perceive improvement and continue using L5P. CPPs entering the trial completed the neuropathic pain scale (NPS) at entrance and completion of the trial. The senior author also completed a baseline information tool on each CPP entering this naturalistic trial. At the completion of the 3-day trial, the CPPs were asked if they perceived pain improvement with the use of L5P. In the retrospective review, the CPPs were thus segregated into two groups, those with and without perceived clinical improvement, and were statistically compared for available clinical variables. Logistic regression was then utilized to determine which significant independent variables contributed to the correct prediction of perceived improvement. SETTING: Multidisciplinary pain facility. PATIENTS: Patients with chronic pain. RESULTS: Of 362 consecutive CPPs, 114 or 31.5% were deemed candidates for this naturalistic trial. None of the CPPs refused or fulfilled exclusion criteria eliminating them from the trial. The total sample (N = 114) showed statistical improvement on all 10 NPS scales (except scales 4 and 6) plus the NPS 4, NPS nonallodynic 8, and NPS 10. The perceived clinically improved group (N = 87, 76.3% of those entering the trial), also showed perceived improvement on all preceding scales except 4 and 6. The perceived clinically nonimproved group (N = 27, 23.7% of those entering the trial) showed statistical improvement on scales B and NPS 10. Perceived improvement was predicted by the following variables: pain wakes patient up, patch placement not low back, and not in litigation. These variables explained 9.8%, 20%, and 14% of the variance, respectively. Overall, 44.5% of the variance was explained. CONCLUSIONS: A significant percentage of CPPs exposed to an L5P 3-day naturalistic trial perceived clinical improvement. However, this can only be concluded as an initial effect, and whether or not this effect is attributable to L5P cannot be derived from our data as the effect could have been nonspecific. The apparent CPP perceived clinical improvement was not associated with any particular useful clinical indicator. As such, at present, no variable can be recommended for use in selecting CPPs for such a naturalistic L5P clinical treatment trial. However, this study indicates that such a trial can be useful in selecting CPPs who may perceive benefit from L5P.

Administration, Cutaneous↗