Serial Subtraction Research Articles

Correlation of cognitive decline and behavioral changes in patients with presenile and senile onset Alzheimer’s disease

Alzheimer?s disease (AD), the most prevalent dementia, is characterized not only by cognitive but also behavioral changes that pose the heaviest burden to caregivers. Differences in the clinical picture depending on the time of disease onset have been observed. We correlated cognitive and behavioral deficits in patients with presenile- and senile-onset AD to explore the differences. We tested 60 AD patients, 19 male and 41 female, mean age 65.2 years with the Dementia Behavior Disturbance Scale (DBD) and a standard neuropsychological battery. The patients were divided according to their DBD score into two groups: group I - score 0-2 (n=24; 40%), group II - score 3? (n=36; 60%), comparable in disease duration and neurological findings. The cognitive scores were significantly higher in the group with less behavioral changes than in the group with more behavioral changes: Mini Mental State Examination score (p=0.0015), serial subtraction (p=0.0009), block design (p=0.0049), copy of complex figure (p=0.0125), complex visual organization (p=0.0099), divided attention, visual memory and speech comprehension. A significantly higher frequency of behavioral disturbances was registered in patients with senile onset than in the presenile-onset group (p<0.005). There were no sex differences. Our data show a correlation between cognitive decline and behavioral changes in late onset AD patients, indicating that more behavioral disturbances were associated with a more severe degree of cognitive decline, especially in non-verbal functions and attention deficits, compared to early onset patients.

Gait Analysis With Cognitive-Motor Dual Tasks to Distinguish Fallers From Nonfallers Among Rehabilitating Stroke Patients

ObjectivesTo evaluate fall risk in stroke patients based on single- and dual-task gait analyses, and to investigate the difference between 2 cognitive tasks in the dual-task paradigm. DesignProspective cohort study. SettingRehabilitation hospitals. ParticipantsSubacute stroke patients (N=32), able to walk without physical/manual help with or without walking aids, while performing a verbal task. InterventionsNot applicable. Main Outcome MeasuresFunctional gait measures were Functional Ambulation Categories (FAC) and use of a walking aid. Gait measures were evaluated by an electronic walkway system under single- and dual-task (DT) conditions. For the single-task, subjects were instructed to walk at their usual speed. One of the DTs was a verbal fluency dual task, whereby subjects had to walk while simultaneously enumerating as many different animals as possible. For the other DT (counting dual task), participants had to walk while performing serial subtractions. After inclusion, participants kept a 6-month falls diary. ResultsEighteen (56.3%) of the 32 included patients fell. Ten (31.3%) were single fallers (SFs), and 8 (25%) were multiple fallers (MFs). Fallers (Fs) more frequently used a walking aid and more frequently needed an observatory person for walking safely (FAC score of 3) than nonfallers (NFs). Two gait decrement parameters in counting dual task could distinguish potential Fs from NFs: decrement in stride length percentage (P=.043) and nonparetic step length percentage (P=.047). Regarding the division in 3 groups (NFs, SFs, and MFs), only MFs had a significantly higher percentage of decrement for paretic step length (P=.023) than SFs. ConclusionsExamining the decrement of spatial gait characteristics (stride length and paretic and nonparetic step length) during a DT addressing working memory can identify fall-prone subacute stroke patients.

Can cerebellar transcranial direct current stimulation become a valuable neurorehabilitation intervention?

Can cerebellar transcranial direct current stimulation become a valuable neurorehabilitation intervention?

Effects of regular meditative practice on psychological measures of healthy subjects

Introduction: Meditation is described as a method for improving attention and promoting psychological and emotional stability, presenting favorable results on cognitive functions and stress tolerance as well. Recently, studies have shown differences on psychological measurements between meditators and non-meditators. The aim of this study was to investigate the influence of regular practice of meditation on psychological measures of healthy participants in basal conditions or after experimental stress-induction. Methods: Forty-four healthy participants (20 meditators and 24 non-meditators) were evaluated by inventories of life quality, anxiety, mood, sleep quality, depression, and stress. Furthermore, all participants were submitted to working memory tasks (Hanoy tower and Digit Spam) before and after two stress-induction procedures: Stroop Color-word and Serial Subtraction tests. The research protocol was approved by the institutional ethics committee (204/09 - CEP/UFRN, CAAE 0221.0.051.000-09). Results: Our results showed that meditators presented better inventories scores when compared with non-meditators in parameters such as life quality (score 15.6 versus 14.9, p = 0.04), mood (score 6.0 versus 22.5, p = 0.02), and depression (score 2.5 versus 7.0, p = 0.01). Regarding stress levels, 10 % of meditators (against 37.5% of non-meditators) presented low levels of stress (p = 0.04). Moreover, there was an improvement in performance of meditators (23.3 ± 0.8) in relation to non-meditators (19.0 ± 1.0) on digit span task and in Hanoi tower of meditators (165.2 ± 6.1 ) in relation to non-meditation (224.1 ± 13.1) after stress induction. Conclusion: These findings corroborate other studies showing that meditation can provide an improvement in general quality of life as well as the performance of practitioners in memory tasks.

Task-specific facilitation of cognition by cathodal transcranial direct current stimulation of the cerebellum

A role for the cerebellum in cognition is controversial, but it is a view that is becoming increasingly popular. The aim of the current study was to investigate this issue using transcranial Direct Current Stimulation (tDCS) during two cognitive tasks that require comparable motor skills, but different levels of working memory and attention. Three groups of twenty-two participants each performed the Paced Auditory Serial Addition Task (PASAT) and a novel variant of this task called the Paced Auditory Serial Subtraction Task (PASST), together with a verb generation task and its two controls, before and after the modulation of cortico-cerebellar connectivity using anodal or cathodal tDCS over the cerebellum. Participants’ performance in the difficult PASST task significantly improved after cathodal stimulation compared to sham or anodal stimulation. Improvement in the easier PASAT was equal across all three stimulation conditions. Improvement in verbal response latencies were also greatest during the PASST task after cathodal stimulation, compared to sham and anodal stimulation, and became less variable. Results for the verb generation task complimented those for the PASST, such that the rate and consistency of participants’ verbal responses were facilitated by cathodal stimulation, compared to sham and anodal stimulation. These findings suggest that DC stimulation over the right cerebellum affects working memory and attention differently depending on task difficulty. They support a role for the cerebellum in cognitive aspects of behaviour, whereby activity in the prefrontal cortex is likely dis-inhibited by cathodal tDCS stimulation over the right cerebellar cortex, which normally exerts an overall inhibitory tone on the cerebral cortex. We speculate that the cerebellum is capable of releasing cognitive resources by dis-inhibition of prefrontal regions of cerebral cortex, enhancing performance when tasks become demanding.

Plasma 1,8-cineole correlates with cognitive performance following exposure to rosemary essential oil aroma

The mode of influence of the aromas of plant essential oils on human behaviour is largely unclear. This study was designed to assess the potential pharmacological relationships between absorbed 1,8-cineole following exposure to rosemary aroma, cognitive performance and mood. Twenty healthy volunteers performed serial subtraction and visual information processing tasks in a cubicle diffused with the aroma of rosemary. Mood assessments were made pre and post testing, and venous blood was sampled at the end of the session. Pearson correlations were carried out between serum levels of 1,8-cineole, cognitive performance measures and change in mood scores. Here we show for the first time that performance on cognitive tasks is significantly related to concentration of absorbed 1,8-cineole following exposure to rosemary aroma, with improved performance at higher concentrations. Furthermore, these effects were found for speed and accuracy outcomes, indicating that the relationship is not describing a speed-accuracy trade off. The relationships between 1,8-cineole levels and mood were less pronounced, but did reveal a significant negative correlation between change in contentment and plasma 1,8-cineole levels. These findings suggest that compounds absorbed from rosemary aroma affect cognition and subjective state independently through different neurochemical pathways.

Preliminary evidence that acute long-chain omega-3 supplementation reduces cardiovascular reactivity to mental stress: A randomized and placebo controlled trial

ObjectiveExaggerated cardiovascular reactivity predicts cardiovascular morbidity and mortality. Some evidence suggests that omega-3 fatty acids improve cardiovascular function. The objective of this study was to examine the influence of an acute low dose of long-chain omega-3 fatty acids on young, healthy individuals. MethodsParticipants (n=34) were randomly assigned to either 21-days of omega-3 fatty acids (1.4g EPA and DHA) or matched placebo. Cardiovascular measurements were obtained in the laboratory during baseline and during a standard mental arithmetic task, where participants were instructed to engage in serial subtractions by 17s from a four-digit number and cardiovascular reactivity to the task was calculated. ResultsMean arterial pressure reactivity was significantly reduced by supplementation (F(1,32)=5. 12, p=.03, η2=.144) but not by placebo. ConclusionSupplementation of omega-3 fatty acids may reduce cardiovascular reactivity to stress.

Gait assessment in mild cognitive impairment and Alzheimer's disease: The effect of dual-task challenges across the cognitive spectrum

Gait impairment is a prominent falls risk factor and a prevalent feature among older adults with cognitive impairment. However, there is a lack of comparative studies on gait performance and fall risk covering the continuum from normal cognition through mild cognitive impairment (MCI) to Alzheimer's disease (AD). We evaluated gait performance and the response to dual-task challenges in older adults with AD, MCI and normal cognition without a history of falls. We hypothesized that, in older people without history of falls, gait performance will deteriorate across the cognitive spectrum with changes being more evident under dual-tasking. Gait was assessed using an electronic walkway under single and three dual-tasks conditions. Gait velocity and stride time variability were not significantly different between the three groups under the single-task condition. By contrast, significant differences of decreasing velocity (p<0.0001), increasing stride time (p=0.0057) and increasing stride time variability (p=0.0037) were found under dual-task testing for people with MCI and AD. Less automatic and more complex dual-task tests, such as naming animals and serial subtraction by sevens from 100, created the greatest deterioration of gait performance. Gait changes under dual-tasking for the MCI and AD groups were statistically different from the cognitively normal controls. Dual-task assessment exposed gait impairments not obvious under a single-task test condition and may facilitate falls risk identification in cognitively impaired persons without a history of falls.

Mini-Mental State Exam Performance of Older African Americans: Effect of Age, Gender, Education, Hypertension, Diabetes, and the Inclusion of Serial 7s Subtraction Versus "World" Backward on Score

The Mini-Mental State Exam (MMSE) is a clinically ubiquitous yet incompletely standardized instrument. Though the test offers considerable examiner leeway, little data exist on the normative consequences of common administration variations. We sought to: (a) determine the effects of education, age, gender, health status, and a common administration variation (serial 7s subtraction vs. "world" spelled backward) on MMSE score within a minority sample, (b) provide normative data stratified on the most empirically relevant bases, and (c) briefly address item failure rates. African American citizens (N = 298) aged 55-87 living independently in the community were recruited by advertisement, community recruitment, and word of mouth. Total score with "world" spelled backward exceeded total score with serial 7s subtraction across all levels of education, replicating findings in Caucasian samples. Education is the primary source of variance on MMSE score, followed by age. In this cohort, women out-performed men when "world" spelled backward was included, but there was no gender effect when serial 7s subtraction was included in MMSE total score. To ensure an appropriate interpretation of MMSE scores, reports, whether clinical or in publications of research findings, should be explicit regarding the administration method. Stratified normative data are provided.

The Woven EndoBridge Cerebral Aneurysm Embolization Device (WEB II): initial clinical experience

The Woven Endobridge (WEB II) device (Sequent Medical, Inc., Aliso Viejo, CA, USA) is an intra-saccular, oblate, braided-wire embolization device designed to provide flow disruption at the aneurysm neck-parent artery interface. The purpose of this study was to evaluate the acute and short-term performance of the WEB II device regarding the immediacy, degree, and durability of aneurysm occlusion in two patients. The WEB II device was implanted in one patient with an unruptured MCA trifurcation aneurysm and one patient with an unruptured basilar tip aneurysm. The degree of intra-aneurysmal flow disruption was graded based on serial digital subtraction aneurysm angiography performed over 30min immediately following device implantation and at 8weeks. Immediate and 8-week post-treatment CT and 3-T MRI studies were also performed. Delivery and deployment of the WEB II device was technically straightforward and achieved without complications. Neither device required retrieval or repositioning after full deployment. There were no peri-procedural thrombembolic or hemorrhagic complications. In both cases, complete aneurysm occlusion was observed within minutes of device deployment. Short-term angiographic follow-up confirmed stable complete occlusion at 8weeks. Early technical and clinical results from the first WEB II cases have been encouraging and suggest that the intra-saccular deployment of self-expanding, compliant, cylindrical, high-density, braided metallic mesh constructs may represent a feasible approach for the endovascular treatment of cerebral aneurysms.

Temporal discounting and heart rate reactivity to stress

Temporal discounting is the reduction of the value of a reinforcer as a function of increasing delay to its presentation. Impulsive individuals discount delayed consequences more rapidly than self-controlled individuals, and impulsivity has been related to substance abuse, gambling, and other problem behaviors. A growing body of literature has identified biological correlates of impulsivity, though little research to date has examined relations between delay discounting and markers of poor health (e.g., cardiovascular reactivity to stress). We evaluated the relation between one aspect of impulsivity, measured using a computerized temporal discounting task, and heart rate reactivity, measured as a change in heart rate from rest during a serial subtraction task. A linear regression showed that individuals who were more reactive to stress responded more impulsively (i.e., discounted delayed reinforcers more rapidly). When results were stratified by gender, the effect was observed for females, but not for males. This finding supports previous research on gender differences in cardiovascular reactivity and suggests that this type of reactivity may be an important correlate of impulsive behavior.

Source imaging of QEEG as a method to detect awareness in a person in vegetative state

Background: Assessment of awareness in patients with severe brain injury remains subjective, although patients with even limited awareness (e.g. minimal conscious state, MCS) have different prognoses and treatment than those in vegetative state (VS). Recently, task appropriate differential regional activation in VS has been reported using fMRI during mental imagery.Primary objective: Demonstration of conscious awareness in reproducible differential EEG source localization images in a VS patient reflecting requested mental imagery was performed.Methods: A VS patient (with re-test) and a normal control were requested to imagine singing and to mentally perform serial subtraction, while EEG was recorded. QEEG source localization was performed to identify regions of brain activation in response to tasks.Results: Replicable distinctive activation of brain areas appropriate for each task was seen in the VS patient and control. Frequency spectra shifted to beta, with significant source activation in regions including the bilateral anterior cingulate, insula, left caudate and dorsolateral pre-frontal cortex to singing and the putamen, insula, left pre-frontal cortex and right temporal gyrus to subtraction by 7's.Conclusions: Results from this single case suggests the potential utility of QEEG source localization images to detect awareness in patients clinically diagnosed as being in VS. This indicates the possibility that EEG may serve as an important adjunct to the assessment of awareness in patients with disorders of consciousness in the clinical setting.

The effects of IQPLUS Focus on cognitive function, mood and endocrine response before and following acute exercise

BackgroundPhosphatidylserine (PS) is a phospholipid found in cell membranes of most animals and plants. PS has been shown to reduce stress and increase performance in runners, cyclists and golfers. The purpose of this study was to investigate the effects of a PS containing formulation on cognitive function, mood and endocrine response before and after intense resistance exercise.Methods18 lower body, resistance trained, college aged males ingested 14 days of supplement (IQPLUS Focus, providing 400 mg of soy-derived PS) and a Placebo (PL), in a randomized, double-blind, placebo controlled, cross-over manner. Following 14 days of supplementation, participants performed an acute bout of lower body resistance training. Mood (Profile of Mood States, POMS) and cognitive function (Serial Subtraction Test, SST) were measured prior to, 5 minutes after, and 60 minutes after exercise. Venous blood samples were collected prior to, and 5, 15, 25, 40 and 60 minutes after exercise. Blood samples were analyzed for plasma cortisol and testosterone. Data were analyzed using repeated measures ANOVA.ResultsPS supplementation significantly reduced the time needed for a correct calculation on the SST by 20% (reduced by 1.27 s per calculation; PL: 6.4 s, PS: 5.13 s; p = 0.001), and reduced the total amount of errors by 39% (PL: 1.28 + .69, PS: .78 + .27, p = 0.53), and increased the amount of correct calculations by 13% (PL: 22.1 + 2.24, PS: 24.9 + 1.52, p = 0.07) prior to or in response to exercise compared to PL. Following exercise, there was no difference in SST scores between PS and PL. There were no significant changes in regards to mood or endocrine response to exercise as a result of PS supplementation.ConclusionPS supplementation significantly increased cognitive function prior to exercise. Improved cognitive function could benefit athletes and non-athletes alike. PS did not appear to affect mood or endocrine response prior to or following resistance exercise.

Influence of a Dual Task while Stepping Over an Obstacle in the Fall-experienced Elderly People

[Purpose] The purpose of this study was to investigate the influence of a dual-task on movements of stepping over an obstacle by elderly people who had a fall experience in the past year. [Subjects] Subjects were 7 people who had a history of falls and 22 people who had no history of falls in the past year. [Methods] Subjects were divided into fallers group while subjects performed and non-fallers group by based on interview results. We measured toe clearance the single and dual tasks. The single task was a solitary motor task. The dual task consisted of a motor task and a concurrent cognitive task. The motor task was stepping over an obstacle during comfortable gait, and the cognitive task was the serial subtraction of seven from 100. [Results] Two-way ANOVA showed that toe-obstacle distance had a significant interaction effect. [Conclusion] These results suggest that fallers and non-fallers may have different strategies for stepping over an obstacle.

Eye movement sequence generation in humans: Motor or goal updating?

Saccadic eye movements are often grouped in pre-programmed sequences. The mechanism underlying the generation of each saccade in a sequence is currently poorly understood. Broadly speaking, two alternative schemes are possible: first, after each saccade the retinotopic location of the next target could be estimated, and an appropriate saccade could be generated. We call this the goal updating hypothesis. Alternatively, multiple motor plans could be pre-computed, and they could then be updated after each movement. We call this the motor updating hypothesis. We used McLaughlin's intra-saccadic step paradigm to artificially create a condition under which these two hypotheses make discriminable predictions. We found that in human subjects, when sequences of two saccades are planned, the motor updating hypothesis predicts the landing position of the second saccade in two-saccade sequences much better than the goal updating hypothesis. This finding suggests that the human saccadic system is capable of executing sequences of saccades to multiple targets by planning multiple motor commands, which are then updated by serial subtraction of ongoing motor output.

Talking while walking: Cognitive loading and injurious falls in Parkinson's disease

Multitasking has become a way of life, from operating multiple software packages simultaneously on a computer, to carrying on a conversation on a cell phone while driving. Perhaps one of the most common dual tasks performed is talking while walking. In isolation, neither task would be considered difficult to perform, yet when coupled, the relative ease of each task may change. This paper details significant problems that result from injurious falls, and points out the vulnerability of those who have been diagnosed with Parkinson's disease. In addition, it provides an illustrative study that demonstrates the potential danger of talking while walking, especially when the cognitive-linguistic complexity of verbal tasks is manipulated. In this investigation, 25 participants with Parkinson's disease and 13 participants without neurological compromise completed gait tasks while conducting tasks of low (counting by ones), middle (serial subtraction of threes), and high load (alpha-numeric sequencing). The results indicated that cognitive-linguistic demand had an impact on gait, the effects of which were demonstrated in individuals without neurological compromise as well as those with Parkinson's disease. One finding, altered double-support time, distinguished the Parkinson group from the control participants. These results suggest that it might be prudent for healthcare professionals and caregivers to alter expectations and monitor the cognitive-linguistic demands placed on elderly individuals, particularly those with neurological compromise who might be at greater risk for injurious falls.

A New Vascular Pattern for Idiopathic Juxtafoveal Telangiectasia Revealed by the Retinal Function Imager

The Retinal Function Imager (RFI) (Optical Imaging, Rehovot, Israel) is a novel method for assessing retinal blood flow characteristics and demonstrating the dynamics of fine retinal vasculature. The authors report a new pattern of retinal blood flow in five patients with idiopathic juxtafoveal telangiectasia (IJT) type 2. Retinal circulation is imaged using the RFI as a series of high-speed stroboscopically captured fundus photographs. Proprietary software aligns the images, allowing serial subtraction, and creates short video loops that show movement of red blood cells in the small and medium size retinal blood vessels. Ten eyes of five patients with IJT type 2 were examined. In all cases, the RFI demonstrated a common pattern of centripetal vascular flow in the region of telangiectasia. This pattern is unique in its configuration of vascular flow into the focus of the area of telangiectasia. This pattern could not be appreciated on fluorescein angiography. The RFI can detect the specific vascular pattern of the retinal blood flow in eyes of patients with IJT. The ability to characterize such blood flow patterns may aid in identification of ambiguous cases of IJT when the diagnosis is not straightforward.

CONTRIBUTION OF CORE BODY TEMPERATURE, PRIOR WAKE TIME, AND SLEEP STAGES TO COGNITIVE THROUGHPUT PERFORMANCE DURING FORCED DESYNCHRONY

Shiftworkers are often required to sleep at inappropriate phases of their circadian timekeeping system, with implications for the dynamics of ultradian sleep stages. The independent effects of these changes on cognitive throughput performance are not well understood. This is because the effects of sleep on performance are usually confounded with circadian factors that cannot be controlled under normal day/night conditions. The aim of this study was to assess the contribution of prior wake, core body temperature, and sleep stages to cognitive throughput performance under conditions of forced desynchrony (FD). A total of 11 healthy young adult males resided in a sleep laboratory in which day/night zeitgebers were eliminated and ambient room temperature, lighting levels, and behavior were controlled. The protocol included 2 training days, a baseline day, and 7 × 28-h FD periods. Each FD period consisted of an 18.7-h wake period followed by a 9.3-h rest period. Sleep was assessed using standard polysomnography. Core body temperature and physical activity were assessed continuously in 1-min epochs. Cognitive throughput was measured by a 5-min serial addition and subtraction (SAS) task and a 90-s digit symbol substitution (DSS) task. These were administered in test sessions scheduled every 2.5 h across the wake periods of each FD period. On average, sleep periods had a mean (± standard deviation) duration of 8.5 (±1.2) h in which participants obtained 7.6 (±1.4) h of total sleep time. This included 4.2 (±1.2) h of stage 1 and stage 2 sleep (S1–S2 sleep), 1.6 (±0.6) h of slow-wave sleep (SWS), and 1.8 (±0.6) h of rapid eye movement (REM) sleep. A mixed-model analysis with five covariates indicated significant fixed effects on cognitive throughput for circadian phase, prior wake time, and amount of REM sleep. Significant effects for S1–S2 sleep and SWS were not found. The results demonstrate that variations in core body temperature, time awake, and amount of REM sleep are associated with changes in cognitive throughput performance. The absence of significant effect for SWS may be attributable to the truncated range of sleep period durations sampled in this study. However, because the mean and variance for SWS were similar to REM sleep, these results suggest that cognitive throughput may be more sensitive to variations in REM sleep than SWS. (Author correspondence: david.darwent@unisa.edu.au)

INTERINDIVIDUAL DIFFERENCES IN NEUROBEHAVIORAL PERFORMANCE IN RESPONSE TO INCREASING HOMEOSTATIC SLEEP PRESSURE

Neurobehavioral function deteriorates with increasing homeostatic sleep pressure during wakefulness. It has been claimed that some individuals exhibit a quicker rate of such deterioration than others, thus being more vulnerable than others to the detrimental impact of increasing homeostatic sleep pressure. Evidence supporting the claim, however, has been limited by methodological issues. To overcome these limitations, the current study used a 12-calendar-day, 28-h forced desynchrony (FD) protocol (sleep:wake period = 1:2) to study individual differences in the rate of change in neurobehavioral performance with increasing homeostatic sleep pressure. Neurobehavioral performance was assessed with a psychomotor vigilance task and a serial addition subtraction task. A significant performance decline on both tasks was revealed within as short as 17 h of wakefulness. The rates of decline of individual performance trajectories were, however, not different from the group average rate. This suggests that individuals are not differentially vulnerable to the detrimental impact of increasing homeostatic sleep pressure. (Author correspondence: xuan.zhou@unisa.edu.au)

A Method for Serial Selective Arterial Catheterization and Digital Subtraction Angiography in Rodents

Imaging is a key element in the study of many rodent models of human diseases. The application of DSA has been limited in these studies in part because of a lack of a method that allows serial intra-arterial examinations to be performed during an extended period of time. It was our intent to develop and test a method for performing sequential arterial catheterizations and DSA in rats. Using a transfemoral approach, we subjected 12 adult male Harvey rats to 3 sequential DSA examinations during a 6- to 8-week period. At each examination, 2 selective arterial catheterizations and a DSA were performed. Animals were monitored for ill effects, and images from the 3 examinations were compared for quality and the presence of any arterial injury. Ten of the 12 rats survived all 3 examinations. There were no adverse effects noted and no evidence of arterial injury from the examinations. With the technique described, it is possible to perform serial arterial catheterizations and DSA in rats. This technique will be useful as an adjunct in the use of rodents for the study of human diseases.