202 research outputs found
Evidence for a mosaic representation of the body surface in area 3b of the somatic cortex of cat
No full textA discontinuous representation of the forelimb body surface in area 3b is proposed. Two different methods were used: single-neuron receptive-field (RF) mapping in unanesthetized cats (maximal RF) and multiunit RF mapping in deeply anesthetized cats (minimal RF). Ten or more maximal RFs were sampled in each of 14 near-radial microelectrode penetrations. In 6 penetrations, the maximal RFs of all sampled neurons (despite prominent variations in RF size and shape) shared in common a small skin area--termed the "RF center." Each of the remaining penetrations had to be divided into at least two segments (6 penetrations) or three segments (2 penetrations), for all maximal RFs mapped in a segment to include a common skin site. In six penetrations, after maximal RFs were mapped, deep general anesthesia was induced and minimal RFs were mapped in the same penetration at cortical sites separated by 150 microns. Minimal RFs closely matched the RF centers defined by maximal RFs in the same penetration. In penetrations that mapped two or three RF centers, a rapid transition in minimal RF position was detected at the same cortical site where the shift in RF center was detected. Closely spaced penetrations revealed discrete cortical columns, having the size and shape of 350- to 400-microns-diameter irregular hexagons, such that the identical minimal RF was mapped at any site within a column. The forelimb body surface in cat 3b thus appears to be represented by a mosaic of discrete columns--an organization similar to the whisker representation in rodent primary somatosensory cortex
Vibrotactile adaptation fails to enhance spatial localization in adults with autism
No full textA recent study (Tannan et al., 2006) showed that pre-exposure of a skin region to a 5 sec 25 Hz flutter stimulus (“adaptation”) results in an approximately 2-fold improvement in the ability of neurologically healthy human adults to localize mechanical stimulation delivered to the same skin region that received the adapting stimulation. Tannan et al. (Tannan et al., 2006) proposed that tactile spatial discriminative performance is improved following adaptation because adaptation is accompanied by an increase in the spatial contrast in the response of contralateral primary somatosensory cortex (SI) to mechanical skin stimulation – an effect identified in previous imaging studies of SI cortex in anesthetized non-human primates (e.g., Simons et al., 2005; Tommerdahl et al., 2002; Whitsel et al., 1989)
Trends in US Mortality and Effects of Potential Nationwide Interventions on Ambient Levels of Fine Particulate Matter
No full textFine particulate matter (PM2.5) has been consistently shown to be associated with all-cause and cardiorespiratory mortality, such that the United States Environmental Protection Agency (EPA) has declared its relationship with mortality to be causal. The EPA also sets standards to limit ambient concentrations of PM2.5 nationally and any further changes to these standards will require evidence that rigorously demonstrates health benefits. Here, we seek to provide information that will directly inform this decision making process. In aim 1 we proposed a new method to estimate and visualize trends in the natural history of US all-cause and cause-specific mortality, 1968-2016. In aim 2, we assessed how intervening to reduce PM2.5 to below potential future standards (5 and 10 µg/m3) in all US counties 2000-2016 would have changed risk of all-cause and cause-specific mortality, compared to the natural history. These two aims were conducted in a synthetic cohort built to represent the exposure and mortality experience of the resident US population, using mortality and population data from the National Center of Health Statistics. For aim 2, our synthetic cohort was fused to county-specific annual average PM2.5 concentrations, which were estimated using EPA monitor data and geospatial modeling. We used the generalized computational algorithm formula to estimate risk differences comparing the natural history to our two intervention scenarios, accounting for potential confounding by county-level socioeconomic variables. In aim 1, we were able to replicate several of the reported trends in US mortality since 1968, for example, that life expectancy has increased and cardiovascular mortality risk has decreased. In aim 2, we estimated that risk of all-cause mortality by age 80 would unexpectedly increase under both of the stricter PM2.5 standards, driven primarily by an increase in risk of non-cardiorespiratory mortality. Cardiovascular mortality risk by age 85 decreased under both intervention scenarios. However, our results were uninterpretable and likely biased. Even so, our aim 2 analysis provided a new example for how one could directly estimate the effect of setting a new nationwide PM2.5 standard on mortality. We outline ways to improve and refine the proposed approach.Doctor of Philosoph
Response of Anterior Parietal Cortex to Different Modes of Same-Site Skin Stimulation
No full text Tommerdahl, M., K. A. Delemos, O. V. Favorov, C. B. Metz, C. J. Viereck, Jr., and B. L. Whitsel. Response of anterior parietal cortex to different modes of same-site skin stimulation. J. Neurophysiol. 80: 3272–3283, 1998. Intrinsic optical signal (IOS) imaging was used to study responses of the anterior parietal cortical hindlimb region (1 subject) and forelimb region (3 subjects) to repetitive skin stimulation. Subjects were four squirrel monkeys anesthetized with a halothane/nitrous oxide/oxygen gas mixtures. Cutaneous flutter of 25 Hz evoked a reflectance decrease in the sectors of cytoarchitectonic areas 3b and/or 1 that receive input from the stimulated skin site. The intrinsic signal evoked by 25-Hz flutter attained maximal intensity ≤2.5–3.5 s after stimulus onset, remained well maintained as long as stimulation was continued, and disappeared rapidly (usually ≤2–5 s) after stimulus termination. Repetitive skin heating stimuli were delivered via a probe/thermode in stationary contact with the skin (6 temperature ramps/trial; within-trial ramp frequency 0.42 Hz; intertrial interval 180 s; initial temperature 32–36°C; maximal temperature 48–52°C; rate of temperature change 19°C/s). Skin heating led to a large-amplitude reflectance decrease within a zone of area 3a, which neighbored the region in areas 3b/1 that emitted an intrinsic signal in response to same-site 25-Hz flutter in the same subject. In three of four subjects a lower-amplitude decrease in reflectance also occurred in a region of area 4 continuous with the area 3a region that responded maximally to same-site skin heating. The reflectance decrease evoked in areas 3a/4 by skin heating consistently exceeded in both intensity and spatial extent the decrease in reflectance evoked in areas 3b/1 by same-site 25-Hz cutaneous flutter. These findings are viewed as consistent with the proposal that area 3a plays a leading role in the anterior parietal cortical processing of the afferent drive evoked by skin-heating stimuli perceived as painful. In all four subjects the reflectance decrease evoked in areas 3a/4 by skin heating was accompanied by a simultaneous but opposite change in reflectance (a reflectance increase) within a large territory located immediately posterior to the regions that responded with a decrease in reflectance—an observation that raised the possibility that skin heating evoked opposing influences on the activity of area 3a and 3b/1 regions that receive input from the stimulated skin site. This was evaluated with the method of correlation mapping. The observations obtained with correlation mapping appear consistent with demonstrations by others that skin-heating stimuli perceived as painful by conscious subjects suppress/inhibit the anterior parietal response to innocuous mechanical skin stimulation. The opposing (relative to the response of area 3a) optical response of area 1 and/or area 3b during skin heating stimulation is attributed to suppression/inhibition of area 1 and/or area 3b neuron activity. </jats:p
Imaging the Responding Neuronal Population with 14c-2-Deoxyglucose: The Somatosensory Cerebral Cortical Signature of a Tactile Stimulus
No full textImaging the Responding Neuronal Population with 14C-2-Deoxyglucose: The Somatosensory Cerebral Cortical Signature of A Tactile Stimulus
No full textHeart rate variability and target organ damage in hypertensive patients
No full textBackground:
We evaluated the association between linear standard Heart Rate Variability (HRV) measures and vascular, renal and cardiac target organ damage (TOD).
Methods:
A retrospective analysis was performed including 200 patients registered in the Regione Campania network (aged 62.4 ± 12, male 64%). HRV analysis was performed by 24-h holter ECG. Renal damage was assessed by estimated glomerular filtration rate (eGFR), vascular damage by carotid intima-media thickness (IMT), and cardiac damage by left ventricular mass index.
Results:
Significantly lower values of the ratio of low to high frequency power (LF/HF) were found in the patients with moderate or severe eGFR (p-value < 0.001). Similarly, depressed values of indexes of the overall autonomic modulation on heart were found in patients with plaque compared to those with a normal IMT (p-value <0.05). These associations remained significant after adjustment for other factors known to contribute to the development of target organ damage, such as age. Moreover, depressed LF/HF was found also in patients with left ventricular hypertrophy but this association was not significant after adjustment for other factors.
Conclusions:
Depressed HRV appeared to be associated with vascular and renal TOD, suggesting the involvement of autonomic imbalance in the TOD. However, as the mechanisms by which abnormal autonomic balance may lead to TOD, and, particularly, to renal organ damage are not clearly known, further prospective studies with longitudinal design are needed to determine the association between HRV and the development of TOD
Variability in somatosensory cortical neuron discharge: effects on capacity to signal different stimulus conditions using a mean rate code
No full text 1. The present study is based on the demonstration (8, 9) that the relationship between mean interval (MI) and standard deviation (SD) for stimulus-driven activity recorded from SI neurons is well fitted by the linear equation SD = a X MI + b and on the observations that the values of the slope (a) and y intercept (b) parameters of this relationship are independent of stimulus conditions and may vary widely from one neuron to the next (8). 2. A criterion for the discriminability of two different mean firing rates requiring that the mean intervals of their respective interspike interval (ISI) distributions be separated by a fixed interval (expressed in SD units) is developed and, on the basis of this criterion, a graphical display of the capacity of a neuron with a known SD-MI relationship to reflect a change in stimulus conditions with a change in mean firing rate is derived. Using this graphical approach, it is shown that the parameters of the SD-MI relationship for a single neuron determine a range of firing frequencies, within which that neuron exhibits the greatest capacity to signal differences in stimulus conditions using a frequency code. 3. The discrimination criterion is modified to incorporate the changes in the symmetry of the ISI distribution observed to accompany changes in mean firing rate. It is shown that, although the observed symmetry changes do influence the capacity of a cortical neuron to signal a change in stimulus conditions with a change in mean firing rate, they do not alter the range of firing rates (determined by the parameters of the SD-MI relationship) within which the capacity for discrimination is maximal. 4. The maximal number of firing levels that can be distinguished by a somatosensory cortical neuron (using the same discrimination criterion described above) discharging within a specified range of mean frequencies also is demonstrated to depend on the parameters of the linear equation which relates SD to MI. 5. Two approaches based on the t test for differences between two means are developed in an attempt to ascertain the minimum separation of the mean intervals of the ISI distributions necessary for two different mean firing rates to be discriminated with 80% certainty. </jats:p
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