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PubMedDate not supplied

Effect of voluntary muscle contraction on the startle response to auditory stimuli.

Startle reflex responses were studied in 15 normal human subjects using weak (88 dB) and strong (114 dB) auditory stimuli in the orbicularis oculi, masseter, sternocleidomastoid, trapezius, deltoid, biceps, forearm flexors and quadriceps muscles. With the subjects in the relaxed state, no consistent responses were seen with the weak stimuli, and with the strong stimuli responses were only present in orbicularis oculi muscles. When the above muscles were in a state of voluntary contraction, the strong stimuli produced complex responses which were not always excitatory in nature, with muscle relaxation being noted in a number of stimulation sequences. Repetitive weak and strong stimuli were used to study habituation effects in the orbicularis oculi muscles. The repetitive strong stimuli produced a wide range of response patterns, indicating a high inter-individual variability in habituation. In two subjects, no habituation effects were present. Our study supports the high intra-individual variability of the startle response, and suggests that this response is affected by the state of muscle contraction at the time of stimulation. Startle response is more easily elicited in a state of muscular contraction. Future studies of startle reflex should take this into consideration.

Acoustic Stimulation↗
PubMed2006

Perceptions of social capital and the built environment and mental health.

There has been much speculation about a possible association between the social and built environment and health, but the empirical evidence is still elusive. The social and built environments are best seen as contextual concepts but they are usually estimated as an aggregation of individual compositional measures, such as perceptions on trust or the desirability to live in an area. If these aggregated compositional measures were valid measures, one would expect that they would evince correlations at higher levels of data collection (e.g., neighbourhood). The aims of this paper are: (1) to investigate the factor structure of a self-administered questionnaire measuring individual perceptions of trust, social participation, social cohesion, social control, and the built environment; (2) to investigate variation in these factors at higher than the individual level (households and postcodes) in order to assess if these constructs reflect some contextual effect; and (3) to study the association between mental health, as measured by the General Health Questionnaire-12 (GHQ-12), and these derived factors. A cross-sectional household survey was undertaken during May-August 2001 in a district of South Wales with a population of 140,000. We found that factor analysis grouped our questions in factors similar to the theoretical ones we had previously envisaged. We also found that approximately one-third of the variance for neighbourhood quality and 10% for social control was explained at postcode (neighbourhood) level after adjusting for individual variables, thus suggesting that some of our compositional measures capture contextual characteristics of the built and social environment. After adjusting for individual variables, trust and social cohesion, two key social capital components were the only factors to show statistically significant associations with GHQ-12 scores. However, these factors also showed little variation at postcode levels, suggesting a stronger individual determination. We conclude that our results provide some evidence in support of an association between mental health (GHQ-12 scores) and perceptions of social capital, but less support for the contextual nature of social capital.

Adult↗
PubMed1998

Predicting posttraumatic stress symptoms in mothers and fathers of survivors of childhood cancers.

OBJECTIVE: To predict posttraumatic stress symptoms in parents of survivors of childhood cancer, using as predictors the following: personality (trait anxiety); current family and individual variables (perceived life threat, perceived treatment intensity, life events, family functioning, and social support); posttreatment variables (time since treatment ended, child anxiety, medical sequelae); and treatment events (age at diagnosis, radiation therapy, intensity of treatment). METHOD: Mothers and fathers of 6- to 20-year-old survivors of childhood cancer (n = 331 families) completed a questionnaire battery in this two-site study. The outcome variable was the Posttraumatic Stress Disorder Reaction Index. Multiple regressions and path analyses were used to test the model. RESULTS: For both mothers and fathers, anxiety was the strongest predictor of posttraumatic stress symptoms. The current family and individual variables also contributed significantly, particularly with respect to the individual contributions of perceived life threat, perceived treatment intensity, and social support. Objective medical data did not contribute to posttraumatic stress symptoms. CONCLUSIONS: Parental anxiety warrants attention throughout the course of treatment for childhood cancer and after treatment ends. Beliefs about past and present life threats associated with cancer treatment and family and social support are other important targets for intervention.

Adolescent↗
PubMed1998

[Analysis of arterial pressure variability among individuals with white coat hypertension and essential arterial hypertension using blood pressure ambulatory monitoring].

OBJECTIVES: To compare patients with "white coat" hypertension (WCH) and essential hypertension for variability in blood pressure (BP) taken in the clinic. DESIGN: Crossover study. SETTING: La Orden Health Centre, Huelva. PATIENTS: 126 people with light-to-moderate hypertension, de novo or not, being monitored but not treated by drugs. Two groups were formed: WCH defined by mean daily systolic and distolic pressures below 135 and 85 mmHg, and hypertension when the BP was over 140 and/or 90 mmHg. MEASUREMENTS AND MAIN RESULTS: BP was taken in the clinic in two periods: by day (7 a.m. to midnight) and at night (00.01 to 06.59), with readings every 15 and 30 minutes, respectively. Variability was compared by analysing: a) variability indices (VI), and b) coefficients of variation (CV) in BP. A regression test and multiple correlation was used. Both groups (hypertension and WCH) contained 63 people (average age: 53.4 +/- 10 and 50 +/- 10). No significant differences between the two groups in the VI were observed, except greater variability in the VI of the nocturnal systolic pressure of the hypertension group. The CV was higher in the WCH group for all pressures, with differences for 24-hour and day-time systolic pressure. The VI of systolic pressure correlated significantly with its overall clinical systolic pressure in the 24-hour period, with the day and night-time readings and with age in the day-time period. CONCLUSIONS: Variability in the blood pressure of people with essential hypertension and WCH does not differ. Variability in systolic pressure shows positive correlation with clinical systolic pressure and, to a lesser extent, with age.

Blood Pressure Monitoring, Ambulatory↗
PubMed1990

Population pharmacokinetics of phenytoin in Singapore Chinese.

The pharmacokinetics of phenytoin was studied in 66 epileptic Chinese children and adults. The data were analysed by the population approach, using the non-linear mixed effect model, in the MULTI (ELS) program. There was no age or gender-related effect on either the apparent maximum elimination rate (kmax) or Michaelis-Menten constant (KM). Kmax was related to body weight 0.656. The population pharmacokinetics was similar in children and adults. Kmax and KM were estimated to be 30.72 mg.kg-0.656 day-1 and 2.307 mg.l-1, respectively. Kmax was higher than reported values, and KM was comparable to that reported in a study in Japanese, but was much lower than that reported in studies of European patients. The inter-individual variability of KM (CV 65.58%) was substantially higher than that of kmax (CV 28.49%), and the residual (intra-individual) variability was found 21.33% (CV).

Adolescent↗
PubMed1998

Long-term pharmacokinetics of clozapine.

BACKGROUND: Previous studies of clozapine pharmacokinetics have shown a wide intra- and inter-individual variability of plasma levels in patients on stable clozapine doses. We investigated dose-plasma level relationships and intra-individual variability of plasma levels during maintenance treatment with clozapine. METHOD: Forty-one patients on clozapine were followed for 26 weeks with repeated plasma level measurements and assessments of co-medication and clinical symptoms. In a second step, 15 patients on stable clozapine doses between treatment Weeks 12 and 52 were followed in the same way. Coefficient of variation was used as a parameter of plasma level deviation. RESULTS: Dose-plasma level correlations stayed significant from Week 6 to Week 26 (n = 41). The group of patients followed up to Week 52 showed a mean intra-individual coefficient of variation of 52.8% (s.d. = 20.6), and remained stable psychopathologically. CONCLUSIONS: Even though clozapine plasma levels may show a significant degree of variation, this is not necessarily reflected in a change in psychopathology.

Adult↗
PubMed2001

Olanzapine disposition in humans is unrelated to CYP1A2 and CYP2D6 phenotypes.

OBJECTIVE: Limited data suggest that CYP1A2 and CYP2D6 are involved in the metabolism of olanzapine. The purpose of this study was to further elucidate the role of these enzymes in the disposition of olanzapine in vivo. METHODS: Seventeen healthy non-smoking male volunteers were included in the study. Five subjects were CYP2D6 poor metabolisers (PMs), and 12 were CYP2D6 extensive metabolisers (EMs). All subjects received a single oral dose of 7.5 mg olanzapine, and serum concentrations were measured for 96 h using gas chromatography. A cross-over study was undertaken in the 12 CYP2D6 EMs who at least 2 weeks before or after the olanzapine dose received a single oral dose of 200 mg caffeine. The concentrations of caffeine and paraxanthine were measured in saliva 10 h after caffeine intake, and the paraxanthine/caffeine ratio was calculated as a measure of CYPIA2 activity. RESULTS: A threefold inter-individual variability in oral clearance (CLoral) and maximum serum concentration (Cmax) of olanzapine was observed and a 2.3-fold inter-individual variability in CYPIA2 activity. There was no significant correlation between CYP1A2 activity and oral clearance of olanzapine (r=-0.19, P=0.56). Moreover, there were no significant differences in any of the olanzapine pharmacokinetic parameters between the CYP2D6 PMs and EMs (CLoral=0.246 l h(-1) kg(-1) and 0.203 l h(-1) kg(-1), respectively, P=0.30). CONCLUSION: Neither CYP1A2 nor CYP2D6 seem to have a dominating role in olanzapine biotransformation after intake of a single dose.

Adult↗
PubMed1994

Metabolism of nicotine to cotinine studied by a dual stable isotope method.

OBJECTIVES: (1) To determine the disposition kinetics of nicotine and cotinine, including the fractional conversion of nicotine to cotinine, (2) to compare the disposition kinetics of deuterium-labeled and unlabeled cotinine, and (3) to develop a pharmacokinetically based method for estimating daily intake of nicotine from cigarette smoking. STUDY DESIGN: Twenty cigarette smokers received a combined infusion of deuterium-labeled nicotine (d2) and cotinine (d4). Six nonsmokers received a combined infusion of unlabeled cotinine, cotinine-d2 and cotinine-d4. Daily intake of nicotine was estimated with use of the plasma cotinine concentration during ad libitum smoking, clearance of labeled cotinine, and fractional conversion of nicotine to cotinine. RESULTS: The kinetics of labeled versus unlabeled cotinine and of cotinine in smokers versus nonsmokers were similar. On average, 72% of nicotine was converted to cotinine, with a range from 55% to 92%. Subjects with lower clearances of nicotine had lower fractional conversion of nicotine to cotinine, indicating that this is the most rapid of the proximate metabolic pathways for nicotine. The equation for estimating daily intake of nicotine from smoking was: Dnic (mg/24 hr) = K x (Plasma Cot) (ng/ml), where K averaged 0.08, with a range from 0.047 to 0.102. Individual variability in the clearance of cotinine (coefficient of variation, 27.5%) accounts for more of the variability in K than does variability in the fractional conversion of nicotine to cotinine (coefficient of variation, 12.3%). CONCLUSIONS: Our study provides quantitative data on individual variability in the extent of C-oxidation of nicotine to cotinine and a quantitative perspective on the use of plasma cotinine as an indicator of daily intake of nicotine from tobacco.

Adult↗
PubMed1976

The TSH response to thyrotropin-releasing hormone (TRH) in young adult men: intra-individual variation and relation to basal serum TSH and thyroid hormones.

The response of serum TSH to duplicate tests with each of two doses of TRH (30 mug and 500 mug) was studied in 22 normal young adult men. The mean intra-individual variability of the response assessed by duplicate testing (coefficient of variation) was 17% but was as high as 63% in individual subjects. While the actual range of peak TSH values after 500 mug TRH was 2.7-19.5 muU/ml, those subjects (3 of 22) with a peak TSH value between 2 and 5 muU/ml on one occasion were all greater than 5 muU/ml on another. Thus, despite the intra-individual variability, a peak TSH value after 500 mug TRH of less than 2 muU/ml indicates TSH deficiency and greater than 5 muU/ml indicates normal TSH reserve. A peak value of 2-5 muU/ml is an indication for retesting;; a peak TSH value greater than 5 muU/ml on retesting indicates normal TSH reserve. The use of the maximal increase in TSH above basal values (max deltaTSH) did not have a clear advantage over the use of the peak TSH value although a max deltaTSH greater than 4 muU/ml was equivalent to a peak value greater than 5 muU/ml. No information was lost by using only the TSH value at 30 min after TRH instead of multiple samples. In using these values differences in assay technique should be considered; for example, the use of human TSH standard MRC 68/38 instead of human TSH standard A (MRC 63/14) causes a fall of about 1/3 in measured serum values. The overall TSH response to 500 mug TRH was statistically greater than the response to 30 mug TRH (P less than 0.01); however, in 10 of 22 subjects the response to the two doses was about the same, suggesting that the dose response of TSH to TRH, between 30 mug and 500 mug TRH, is quite shallow. The TSH value 60 min after 500 mug TRH was within 2 muU/ml of the peak TSH value in 12 of 22 subjects on at least one occasion; this pattern of a delayed fall is a normal variant. The peak TSH response to TRH correlated well with the basal level of TSH (P less than 0.001) and thus can be considered a magnifier of the basal level of TSH in normal subjects. While the peak TSH value did not correlate with the basal level of T3, there was a moderate negative correlation of the peak TSH value with the basal level of T4 (P less than 0.02), suggesting that the concentration of serum T4 within the normal range is a determinant of TSH secretion.

Adolescent↗
PubMed2005

Reproducibility of heart rate variability and blood pressure variability in individuals with spinal cord injury.

Individuals with spinal cord injury (SCI) are prone to orthostatic intolerance and an increased risk of cardiovascular disease. The use of heart rate variability (HRV) and blood pressure variability (BPV) as indices of cardiovascular regulation would be valuable in this population; however, their reproducibility has yet to be tested in those with SCI. The purpose of this study was to examine the day-to-day reproducibility of resting HRV and BPV in individuals with SCI. Ten individuals (age 35.9 +/- 13.2 yrs) with chronic (5.4 +/- 7.7 years post injury) SCI (C4-T12; ASIA A-C) participated. On two occasions within a two-week period, 10-minute supine electrocardiogram and Finapres blood pressure recordings were obtained during spontaneous breathing. Computer software calculated frequency domain measures of HRV and BPV (Low frequency (LF) power, High frequency (HF) power, and LF:HF ratio). Intraclass correlations coefficients (R) were used as an index of day-to-day reproducibility, and analyses were conducted on all participants and only those with tetraplegia. For HRV, measures of heart rate, LF, and LF:HF were found to be highly reproducible (R = 0.82-0.88); however, the reproducibility of HF was found to be poor (all participants: R = 0.53, tetraplegia: R = 0.66). Measures of blood pressure as well as systolic BPV also showed high reproducibility (R = 0.72-0.93). Measures of diastolic BPV were less reproducible but still acceptable (R = 0.71-0.89) with the exception of LF:HF(DBP) (R = 0.51). In conclusion, despite the autonomic dysfunction associated with SCI, measures of HRV and BPV may still be used as reproducible indices of autonomic cardiovascular regulation in this population.

Adult↗
PubMed2006

Bromide as a marker to measure adherence to drug therapy.

OBJECTIVE: Several methods have been described to measure adherence to prescribed drug therapy. However, most of these have been shown to be inaccurate. Bromide is an anion that is readily absorbed in the gut and has an elimination half-life of about 12 days. In the present study, we investigated the pharmacokinetic properties of bromide with the objective to use it as a measure of drug adherence. METHODS: Three groups of each 8 healthy volunteers took 15, 24 or 30 mg potassium bromide, respectively, daily for 20 weeks. Serum concentrations of bromide were measured every two weeks. RESULTS: There was a linear relationship between the daily dosage taken and the mean increase of bromide concentration. In every group considerable inter-individual variability was seen. Correction for body weight resulted in an improved correlation between daily bromide dose and increase in concentration (r=0.78, p<0.01). CONCLUSIONS: Unfortunately, the inter-individual variability in clearance of bromide was considerable. This limits the use of bromide to primarily measuring adherence in individual patients during long term follow-up. Bromide appears to be a potentially useful marker to be added to drugs for assessment of individual adherence to long term drug therapy. This needs to be investigated in various patients, particularly for patients with relatively asymptomatic diseases (e.g. hypertension).

Bromides↗
PubMed2001

[Application of population pharmacokinetic approach to clinical evaluation of anticancer agents].

Population pharmacokinetics deals with the typical profiles and the inter- and intra-individual variability in the target patient population to which the drug is applied. It also describes factors that can affect the inter-individual variability in pharmacokinetics, including physiological, pathological, genetic, and external factors. The sample population is the actual patients with a variety of backgrounds, which enables us to analyze the influences of several factors such as severity of illness, advanced age, childhood, and renal or hepatic dysfunction, and also to identify the special populations where dose adjustment is needed. Pharmacokinetic and pharmacodynamic information are useful to a rational dosage regimen. The findings obtained by the population pharmacokinetic and pharmacodynamic analysis, provide an advice about whether a dosage regimen should be individualized in all patients or in identified special populations, together with how to adjust the dose. The study design for population pharmacokinetic analysis is called "pharmacokinetic screen", where drug concentration data are collected from a large number of patients while only a few blood samples are taken from individual patients. The population pharmacokinetic approach is useful not only for establishing the rationale dosage regimen but also for international exchange of clinical data in the global drug development.

Antineoplastic Agents↗
PubMed1998

Effects of repeated seizure induction on seizure activity, post-ictal and interictal behavior.

Individual variability and numerous interactions between pharmacokinetics, pharmacodynamics, and homeostatic factors complicate the study of the anticonvulsant effect in animal models of seizure activity. In theory, both individual variability and the contribution of these factors to the anticonvulsant effect can be determined by following the time course of the pharmacological response and the corresponding plasma concentrations in individual animals. Currently, there are several formal pharmacokinetic-pharmacodynamic models available for the analysis of such data, which yield accurate estimates of drug intrinsic activity and potency. However, most models of seizure activity are not suited for such an approach, either because they can be applied only once, or because the expression of seizures is not constant over time. In addition, the induction of seizures constitutes repeated jeopardy to the animals, which may profoundly change behavior and interfere in the anticonvulsant response as well as in different physiological processes. In this paper, we compare ictal, post-ictal, and interictal behavior in three different models of seizure activity in rats, namely, the electroconvulsive shock, amygdala kindling and the cortical stimulation model (CSM). The methods were compared in the same way as they are currently in use for the assessment of antiepileptic drug effect. Our results show that repeated seizure activity induced by cortical stimulation does not exacerbate ictal activity (eye closure, jerk, gasp, forelimb clonus, and hind-limb tonus) nor post-ictal behavior (chewing and freezing), while producing less serious changes in interictal behavior (walk, lean, upright rearing, exploratory, grooming, and rest) than kindling or electroconvulsive shock. We conclude that seizures induced by cortical stimulation are reproducible and qualitatively similar to kindling seizures. Our results also suggest that the electroconvulsive shock model is not suited for pharmacokinetic-pharmacodynamic studies and that the assessment of interictal behavior may contribute to the evaluation of overall antiepileptic drug effect in seizure disorders.

Analysis of Variance↗
PubMed2005

Individual venom variability in Crotalus durissus ruruima snakes, a subspecies of Crotalus durissus from the Amazonian region.

Venoms of six specimens of Crotalus durissus ruruima snakes from the same geographical site in the Brazilian State of Roraima, were individually assayed for their main pharmacological properties. Quantitative and qualitative differences were found and the presence of crotoxin-like isoforms in these venoms was indicated. Our findings corroborate the existence of a considerable intrapopulational variability in C. d. ruruima venoms, and the importance of using a pool of venoms for antivenom production, in general, in order to assure the neutralization of the maximum possible number of toxins from a given species.

Animals↗
PubMed1990

Ergonovine maleate test detects anginal patients with poorly reproducible exercise tests.

The aim of the study is to evaluate the reproducibility of exercise testing and to determine whether there is any correlation between the reproducibility of exercise test and response to the ergonovine maleate test. Thirty-eight patients with mixed angina and documented coronary artery disease underwent an ergonovine maleate test and four exercise tests on consecutive days in the same basal conditions. The ergonovine test was positive in 20 patients (Group I) and negative in 18 patients (Group II). There were no significant differences in the clinical and angiographic data of the two groups. All 152 exercise tests were positive. The variability of the response of the repeated tests was assessed by means of an analysis of the following parameters: heart rate, blood pressure, rate-pressure product, watts, and minutes were recorded at the onset of ischemia (ST decreases greater than or equal to 0.1 mV). Range (maximal-minimal obtained value), ratio between range and maximal obtained value, and coefficient of variation (standard deviation/mean of the four parameters) were calculated for each patient. The analysis of these values demonstrated that while the test was reproducible in some patients, a high individual variability was present in others. Moreover, the individual variability results were higher in Group I than in Group II, with a statistically significant difference for all considered parameters. In conclusion, it is possible to have a poorly reproducible exercise test in patients with mixed angina. The correlation between a positive ergonovine test and a poorly reproducible exercise test suggests that abnormal coronary vasomotion may sometimes be present during exercise and may affect the reproducibility of the test.

Adult↗
PubMed2002

Prediction of tracheal tube size in children using multiple variables.

BACKGROUND: Tracheal tube (TT) size selection in children is important to avoid complications. Formulae utilizing age and physical characteristics to predict appropriate tube size are not entirely predictive. METHODS: Using an automated anaesthesia record keeper database, the anaesthetic records of 8504 children, aged up to 7 years, who required tracheal intubation, were reviewed. Age, height and weight data were related to TT size. The total number of patients whose age, height and weight were independently available was 8396, 3929 and 7823, respectively. The number having all three variables was 3814. A linear regression analysis was performed for patients with all three variables and for each variable individually. RESULTS: Tracheal tube size is best predicted using multivariate analysis and, for any child aged up to 7 years, is represented by the formula: 2.44 + (age x 0.1) + (height x 0.02) + (weight x 0.016). Formulae utilizing these variables individually are also reviewed. CONCLUSIONS: Prediction of TT size is best accomplished using multiple variables. Further prospective study is suggested.

Age Factors↗
PubMed2001

Longitudinal study of urinary 8-hydroxy-2'-deoxyguanosine excretion in healthy adults.

Numerous studies have investigated the urinary excretion of 8-hydroxy-2'-deoxyguanosine (8-OHdG) as a biomarker for the assessment of oxidative DNA damage in humans. In this study, we performed six consecutive series of measurement of urinary levels of 8-OHdG in 68 healthy probands, in order to provide information on the intra- and inter-individual variability of 8-OHdG and to estimate the influence of smoking, age, sex, body weight and body mass index (BMI) on the excretion of 8-OHdG. The intra-individual coefficient of variation (CV) of urinary 8-OHdG/24 h ranged from 0.18 to 1.06 (mean CV = 0.48). Women excreted significantly lower amounts of 8-OHdG/24 h than men, but the difference lost its significance when the body weight or urinary creatinine were used as covariates. By multiple linear regression analysis significant correlations between the mean individual levels of 8-OHdG/24 h excretion and urinary creatinine (rp = 0.61), and cotinine (rp = 0.27) have been observed, whereas no statistically significant effect of age, body weight and BMI was found. The 8-OHdG/creatinine ratio was found to be significantly increased in 23 smokers (1.95 +/- 0.40 mumol/mol) opposed to 45 non-smoking probands (1.62 +/- 0.50 mumol/mol), which is in good agreement with previously published data. No effect of passive smoking on the excretion of 8-OHdG was found. From our data we conclude that the intra-individual variability of urinary 8-OHdG excretion has been underestimated so far, indicating that values of 8-OHdG measured by single spot monitoring are not representative for individual base levels.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed1993

Neural bases of visual deficits during aging.

Visual abilities decline during normal (non-pathological) aging. Many of these visual declines cannot be attributed to optical changes and must therefore be due to changes in the retina or central visual pathways. These include declines in visual acuity and spatial contrast sensitivity (especially under low luminance levels), suprathreshold contrast vision and contrast gain, temporal-frequency contrast sensitivity and resolution, spatial-temporal interactions, hyperacuity, binocular processing, and sensitivity to motion. Certain aspects of these vision deficits and comparisons with neurophysiological and lesion-behavior studies in monkeys suggest hypotheses about the nature and location (e.g. magnocellular vs parvocellular pathways, specific visual structures, and so on) of the neural deficits. Despite the well-documented psychophysical deficits, available anatomical studies in humans and monkeys suggest that aging has only relatively minor effects on the retino-geniculo-striate pathway. Retinal photoreceptor losses are relatively restricted to rods, and there is compensation among the remaining rods for those that are lost. Although some retinal ganglion cells appear to be lost, the loss is small relative to individual-to-individual variability. In addition, there appear to be no massive cell losses in the LGN or striate cortex. Physiological results in the monkey LGN suggest that the functional properties of LGN neurons, and therefore their retinal inputs, are not significantly affected by aging. Retinal pattern-evoked ERG studies in humans likewise suggest that the physiological properties of the retina are little affected by aging. Comparisons between pattern-evoked ERG and cortical evoked potentials in the same individuals suggest that some neural change occurs between the retina and striate cortex, but the location and nature of this change is not known. Thus, we are far from being able to answer the question, What are the neural bases of visual deficits during aging? There are several possible reasons for this: (1) The neurobiological methods that have been brought to bear on the question have been fairly limited. (2) Investigations of neural changes may not have been guided sufficiently by what is known about the psychophysical changes that occur with aging. (3) Existing studies may not have examined the correct locations in the visual system. (4) There is large individual-to-individual variability in the effects of aging and, with the small samples of individuals that typically are available in neural studies of aging, the variability could obscure detection of aging-related changes. Suggestions are offered for ways in which future research can solve these problems.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗