Aging and cognition

Disease Burden Affects Aging Brain Function

BACKGROUND

Most older adults live with multiple chronic disease conditions, yet the effect of multiple diseases on brain function remains unclear.

METHODS

We examine the relationship between disease multimorbidity and brain activity using regional cerebral blood flow (rCBF) 15O-water PET scans from 97 cognitively normal participants (mean baseline age 76.5) in the Baltimore Longitudinal Study of Aging (BLSA). Multimorbidity index scores, generated from the presence of 13 health conditions, were correlated with PET data at baseline and in longitudinal change (n=74) over 5.05 (2.74 SD) years.

RESULTS

At baseline, voxel-based analysis showed that higher multimorbidity scores were associated with lower relative activity in orbitofrontal, superior frontal, temporal pole and parahippocampal regions, and greater activity in lateral temporal, occipital and cerebellar regions. Examination of the individual health conditions comprising the index score showed hypertension and chronic kidney disease individually contributed to the overall multimorbidity pattern of altered activity. Longitudinally, both increases and decreases in activity were seen in relation to increasing multimorbidity over time. These associations were identified in orbitofrontal, lateral temporal, brainstem, and cerebellar areas.

CONCLUSION

Together, these results show that greater multimorbidity is associated with widespread areas of altered brain activity, supporting a link between health and changes in aging brain function.

Cerebral Vascular Reactivity in Frail Older Adults with Vascular Cognitive Impairment

Background: Frailty, a state of increased vulnerability, could play a role in the progression of vascular dementia. We aim to describe the changes in cerebrovascular reactivity of older adults with frailty and vascular-type mild cognitive impairment (MCIv). Methods: This was a cross-sectional study. A comprehensive geriatric assessment, neuropsychological evaluation, and transcranial Doppler ultrasound (TCD) was performed on 180 participants who were allocated into four groups: healthy (n = 74), frail (n = 40), MCIv (n = 35), and mixed (frail + MCIv) (n = 31). ANOVA and Kruskal–Wallis tests were used for the analysis of continuous variables with and without normal distribution. Multinomial logistic regression was constructed to identify associated covariates. Results: Subjects in the mixed group, compared to healthy group, were older (75.0 ± 5.9 vs 70.3 ± 5.9 years; p < 0.001), showed lower education (9.3 ± 6.4 vs 12.2 ± 4.0 years; p = 0.054), greater frequency of diabetes (42% vs 12%; p = 0.005), worse cognitive performance (z = −0.81 ± 0.94), and reduced left medial-cerebral artery cerebrovascular reactivity (0.43 ± 0.42 cm/s). The mixed group was associated with age (odds ratio (OR) 1.16, 95% Confidence Interval (CI) = 1.06–1.27; p < 0.001), diabetes (OR 6.28, 1.81–21.84; p = 0.004), and Geriatric Depression Scale (GDS) score (OR 1.34, 95% CI = 1.09–1.67; p = 0.007). Conclusions: Frailty among older adults was associated with worse cognitive performance, diabetes, and decreased cerebral blood flow.

Neuroimaging Characteristics of Small-Vessel Disease in Older Adults with Normal Cognition, Mild Cognitive Impairment, and Alzheimer Disease

Introduction

Cerebral small-vessel disease (SVD) represents the most frequent type of vascular brain lesions, often coexisting with Alzheimer disease (AD). By quantifying white matter hyperintensities (WMH) and hippocampal and parietal atrophy, we aimed to describe the prevalence and severity of SVD among older adults with normal cognition (NC), mild cognitive impairment (MCI), and probable AD and to describe associated risk factors.

Methods

This study included 105 older adults evaluated with magnetic resonance imaging and clinical and neuropsychological tests. We used the Fazekas scale (FS) for quantification of WMH, the Scheltens scale (SS) for hippocampal atrophy, and the Koedam scale (KS) for parietal atrophy. Logistic regression models were performed to determine the association between FS, SS, and KS scores and the presence of NC, MCI, or probable AD.

Results

Compared to NC subjects, SVD was more prevalent in MCI and probable AD subjects. After adjusting for confounding factors, logistic regression showed a positive association between higher scores on the FS and probable AD (OR = 7.6, 95% CI 2.7–20, p < 0.001). With the use of the SS and KS (OR = 4.5, 95% CI 3.5–58, p = 0.003 and OR = 8.9, 95% CI 1–72, p = 0.04, respectively), the risk also remained significant for probable AD.

Conclusions

These results suggest an association between severity of vascular brain lesions and neurodegeneration.

Anatomic and physiopathologic changes affecting the airway of the elderly patient: implications for geriatric-focused airway management

There are many anatomical, physiopathological, and cognitive changes that occur in the elderly that affect different components of airway management: intubation, ventilation, oxygenation, and risk of aspiration. Anatomical changes occur in different areas of the airway from the oral cavity to the larynx. Common changes to the airway include tooth decay, oropharyngeal tumors, and significant decreases in neck range of motion. These changes may make intubation challenging by making it difficult to visualize the vocal cords and/or place the endotracheal tube. Also, some of these changes, including but not limited to, atrophy of the muscles around the lips and an edentulous mouth, affect bag mask ventilation due to a difficult face-mask seal. Physiopathologic changes may impact airway management as well. Common pulmonary issues in the elderly (eg, obstructive sleep apnea and COPD) increase the risk of an oxygen desaturation event, while gastrointestinal issues (eg, achalasia and gastroesophageal reflux disease) increase the risk of aspiration. Finally, cognitive changes (eg, dementia) not often seen as related to airway management may affect patient cooperation, especially if an awake intubation is required. Overall, degradation of the airway along with other physiopathologic and cognitive changes makes the elderly population more prone to complications related to airway management. When deciding which airway devices and techniques to use for intubation, the clinician should also consider the difficulty associated with ventilating the patient, the patient's risk of oxygen desaturation, and/or aspiration. For patients who may be difficult to bag mask ventilate or who have a risk of aspiration, a specialized supralaryngeal device may be preferable over bag mask for ventilation. Patients with tumors or decreased neck range of motion may require a device with more finesse and maneuverability, such as a flexible fiberoptic broncho-scope. Overall, geriatric-focused airway management is necessary to decrease complications in this patient population.

Symptom-specific attentional bias to threatening stimuli in obsessive-compulsive disorder

OBJECTIVE

There is mixed evidence as to whether patients with obsessive-compulsive disorder (OCD) have excessive attentional engagement and emotional response to OCD-related stimuli in the environment. Here we investigate the occurrence of an attentional bias toward specific OCD-related stimuli and its relationship with obsessive-compulsive symptom dimensions.

METHODS

Forty-eight patients with OCD participated in an attentional bias task containing OCD- and non-OCD-related stimuli and had their performance compared with that of 24 age-, sex-, and education-matched healthy control subjects. Severity of obsessive-compulsive and comorbid depressive symptoms was assessed using the Obsessive-Compulsive Inventory-Revised and the Beck Depression Inventory, respectively.

RESULTS

Although there were significant and almost significant group effects on the reaction time (RT) toward OCD- and non-OCD-related figures, respectively, no difference between patients with OCD and controls was noted with regard to RT toward OCD-related figures minus RT toward non-OCD-related figures. Nevertheless, within the OCD group, partial correlational analysis controlled for age and severity of depression unveiled positive correlations between (1) obsessional symptoms and RT toward checking-related pictures and (2) ordering symptoms and RT toward ordering-related pictures.

CONCLUSIONS

The positive correlations between RT to content-specific stimuli and the severity of corresponding obsessive-compulsive symptoms suggest that patients with OCD experience difficulty in disengaging attention from personally salient stimuli.

[Anesthesia for geriatric patients. Part 1: age, organ function and typical diseases]

Due to demographic changes in the population of industrial nations the number of elderly patients undergoing elective or emergency procedures will rise significantly in the coming years. Anesthesia for geriatric patients is challenging for the anesthesiologist in many ways: with increasing age numerous physiological changes occur which all lead to a subsequent reduction of physical performance and compensatory capacity of the organism, in many cases additionally aggravated by chronic illness. Subsequently, these age-dependent changes (with or without chronic illness) increase the risk for admission to intensive care units, perioperative death, treatment costs and a prolonged length of hospital stay. Therefore, subtle preoperative assessment and tailored anesthetic management are essential in elderly patients. Part 1 of this continuous education article covers the influence of age on organ functions and describes typical comorbidities which are of high relevance for the perioperative care of geriatric patients. The special features of anesthetic agents and anesthesia management in the elderly will be presented in part 2.

Issues of concern to emergency physicians in pre-retirement years: a survey

BACKGROUND

Many members of the American College of Emergency Physicians are now over the age of 50. Little is known regarding age-specific issues that may impact the careers of emergency physicians in the latter stages of their professional lives.

OBJECTIVES

To determine issues of concern regarding aging and retirement among a cohort of emergency physicians in pre-retirement years.

METHODS

A survey of a randomized sample of 1000 American College of Emergency Physicians members over the age of 55 years was conducted with two separate mailings in the fall of 2006 and winter of 2007. The survey instrument consisted of 30 questions relating primarily to issues of health, finances, and the ability to practice emergency medicine. Four open-ended questions were included at the end of the survey, relating to means of promoting career longevity.

RESULTS

There were 802 usable responses received (response rate 80%). The average respondent was 57 years old and worked 30 clinical and 12 non-clinical h per week. The average estimated time to complete retirement was 7.8 years. Respondents generally viewed themselves as competent clinicians with improved ability to relate to patients and staff and little decline in procedural skills. However, a substantial proportion reported age-related concerns. Seventy-four percent reported less ability to recover from night shifts, 44% reported a higher level of emotional exhaustion at end of shift, 40% reported less ability to manage heavy patient volume, 36% reported less ability to handle stress of emergency medicine, 28% reported health limitations on ability to practice, 28% reported memory somewhat or considerably worse, and 25% reported less ability to incorporate new modalities of diagnosis and treatment. With regard to retirement-related issues, 42% reported concerns about adequate financial preparations and 44% reported concerns regarding loss of identity upon retirement. The practice modifications most commonly reported to impact career longevity were the reduction or elimination of night shifts, a reduction in the number of hours per shift, and an increase in physician and support staffing.

CONCLUSIONS

Respondents to this survey generally viewed themselves as competent, empathic practitioners. Yet a substantial percentage acknowledged at least some degree of cognitive or physical decline. The results suggest a role for the national organizations in emergency medicine in endorsing practice modifications that promote career longevity and clinical competence among its senior members.

Hippocampal neurochemistry, neuromorphometry, and verbal memory in nondemented older adults

BACKGROUND

Characterization of the behavioral correlates of neuromorphometry and neurochemistry in older adults has important implications for an improved understanding of the aging process. The objective of this study was to test the hypothesis that a measure of hippocampal neuronal metabolism was associated with verbal memory in nondemented older adults after controlling for hippocampal volume.

METHODS

4-T MRI, proton magnetic resonance spectroscopy ((1)H MRS), and neuropsychological assessment were conducted in 48 older adults (23 women; mean age 81 years). Average hippocampal N-acetyl aspartate/creatine ratios (NAA/Cr) and hippocampal volumes were obtained. Neuropsychological evaluation included tests of verbal memory (Buschke and Grober Free and Cued Selective Reminding Test-Immediate Recall [FCSRT-IR], Wechsler Memory Scale-Revised Logical Memory subtest) and attention and executive function (Trail Making Test Parts A and B).

RESULTS

Linear regression analysis indicated that after adjusting for age, hippocampal NAA/Cr was a significant predictor of FCSRT-IR performance (beta = 0.38, p = 0.01, R (2) = 0.21). Hippocampal volume was also a significant predictor of FCSRT-IR performance after adjusting for age and midsagittal area (beta = 0.47, p = 0.01, R (2) = 0.24). In a combined model, hippocampal NAA/Cr (beta = 0.33, p = 0.03) and volume (beta = 0.35, p = 0.03) were independent predictors of FCSRT-IR performance, accounting for 30% of the variance in memory.

CONCLUSIONS

These findings indicate that nondemented older adults with smaller hippocampal volumes and lower levels of hippocampal N-acetyl aspartate/creatine ratio metabolites perform more poorly on a test of verbal memory. The integrity of both the structure and metabolism of the hippocampus may underlie verbal memory function in nondemented elderly.

Clinical neurophysiology of aging brain: from normal aging to neurodegeneration

Physiological brain aging is characterized by a loss of synaptic contacts and neuronal apoptosis that provokes age-dependent decline of sensory processing, motor performance, and cognitive function. Neural redundancy and plastic remodelling of brain networking, also secondary to mental and physical training, promotes maintenance of brain activity in healthy elderly for everyday life and fully productive affective and intellectual capabilities. However, age is the main risk factor for neurodegenerative disorders such as Alzheimer's disease (AD) that impact on cognition. Oscillatory electromagnetic brain activity is a hallmark of neuronal network function in various brain regions. Modern neurophysiological techniques including electroencephalography (EEG), event-related potential (ERP), magnetoencephalography (MEG), and transcranial magnetic stimulation (TMS) can accurately index normal and abnormal brain aging to facilitate non-invasive analysis of cortico-cortical connectivity and neuronal synchronization of firing and coherence of rhythmic oscillations at various frequencies. The present review provides a perspective of these issues by assaying different neurophysiological methods and integrating the results with functional brain imaging findings. It is concluded that discrimination between physiological and pathological brain aging clearly emerges at the group level, with applications at the individual level also suggested. Integrated approaches utilizing neurophysiological techniques together with biological markers and structural and functional imaging are promising for large-scale, low-cost and non-invasive evaluation of at-risk populations. Practical implications of the methods are emphasized.

Alpha rhythms in mild dements during visual delayed choice reaction time tasks: A MEG study

Can simple delayed response tasks affect latency and amplitude of magnetoencephalographic midline alpha rhythms (6-12 Hz) in early dementia? We recruited 15 mild Alzheimer's disease (AD) and 10 vascular dementia (VaD) patients (paired mini mental state exam of 17-24). The control groups comprised 18 young and 22 elderly normal subjects. In the first task, a simple "cue" stimulus (one bit) was memorized along a brief delay period (3.5-5.5s) up to a "go" stimulus triggering (right or left) button press. In the second task, the "cue" stimulus remained available along the delay period. Event-related reduction in power of the alpha rhythms indexed the cortical activation (event-related desynchronization, ERD) for the trials associated with correct behavioral responses. Behavioral performances to both tasks were lower in the AD and VaD patients than in the normal subjects. In particular, just four AD and five VaD patients executed a sufficient amount of correct responses for the alpha ERD analysis, so they were included in a unique group. In both tasks, the alpha ERD peak was later in latency in the demented and normal elderly subjects than in the normal young subjects. Furthermore, the alpha ERD peak was stronger in amplitude in the demented patients than in the normal subjects. These results suggest that simple delayed response tasks during physiological recordings are quite difficult for patients even at an early dementia stage. Such difficulty may induce the abnormal amount of the related cortical activation in dementia as revealed by the alpha ERD.

Influence of age on dynamic position sense: evidence using a sequential movement task

Age related changes to the nervous system are well documented. The main objectives of this study were to examine age-associated changes in dynamic position sense and relate these changes to measures of balance and physical function. Two groups of individuals (young <30 years; elderly >60 years) performed an upper extremity movement sequence triggered by a pre-determined target angle during passive rotations of the ankle joint at ten random velocities (10-90 degrees s(-1)). Balance was assessed with a series of timed standing tests. Physical function was assessed with the SF 36 questionnaire. Muscle activity was recorded from the ankle dorsiflexors and plantarflexors during the dynamic position tests. Increased error in the elderly group suggested that dynamic position sense declines with age. Moreover, this decline in dynamic position sense was associated with decreased balance and an impaired perception of physical function. The elderly also co-contracted the ankle plantarflexors and dorsiflexors during the proprioceptive testing, perhaps as a strategy to "gain up" spindle sensitivity. These findings suggest that impaired dynamic position sense of the ankle contributes to alterations in the overall physical function and balance in the elderly. Rehabilitative training methods that improve dynamic position sense of the ankles may improve physical function and balance in the elderly.

Antihypertensive Medication Adherence and Blood Pressure Control in Patients With Psychotic Disorders Compared to Persons Without Psychiatric Illness

The authors compared antihypertensive medication adherence and blood pressure control among middle-aged and older outpatients with schizophrenia and related those with psychotic disorders versus persons without any psychiatric illness. A total of 178 subjects were included in the investigation (89 patients with a psychotic disorder and 89 randomly selected, age-matched comparison subjects). Although the two groups had similar antihypertensive medication adherence, the patients with a psychotic disorder were significantly less likely to have had controlled blood pressure during the 1-year study period. The results highlight the need for clinicians to monitor closely the management of medical comorbidity in patients with schizophrenia and related disorders.

The relationship between impaired glucose tolerance, type 2 diabetes, and cognitive function

The present review integrates findings of published studies that have evaluated the cognitive function of treated and untreated type 2 diabetic patients and provides a detailed overview of the neuropsychological assessments conducted. Cognitive deficits are observed in older people with glucose intolerance or untreated diabetes but these deficits appear to be attenuated by treatments that improve glycemic control. Cognitive decrements in treated type 2 diabetic patients are most consistently observed on measures of verbal memory (35% of the measures) and processing speed (45% of the measures) while preserved function is observed on measures of visuospatial, attention, semantic and language function. Some studies suggest that deficits in cognitive functions are associated with poorer glycemic control. A number of other factors, such as depression, cardiovascular and cerebrovascular disease, increase these deficits. We conclude that, in diabetic patients who achieve and maintain good glycemic control, type 2 diabetes only has a small impact on cognitive functions before the age of 70 years. However, early onset of type 2 diabetes, poor glycemic control and the presence of micro- and macrovascular disease may interact to produce early cognitive deficits. In older adults (70 years and over), diabetes likely interacts with other dementing processes such as vascular disease and Alzheimer's disease to hasten cognitive decline.

The relationships between atherosclerosis, heart disease, type 2 diabetes and dementia

Type 2 diabetes in the elderly is associated with increased incidence of vascular disease, particularly, atherosclerosis of large blood vessels. Together with other risk factors such as dyslipidemia, atherosclerosis increases the risk for coronary heart disease and stroke. Most studies that have examined the impact of type 2 diabetes and other heart disease risk factors on cognitive functions do not provide evidence that heart disease risk factors (with the possible exception of triglycerides) further increase the likelihood of observing cognitive deficits in diabetic patients. However, none of these studies used imaging techniques to evaluate atherosclerosis or evidence of cerebrovascular disease, such as infarctions. The few studies that have included brain imaging suggest that evidence of cerebrovascular disease further increases the risk for dementia in diabetic patients. The results of longitudinal studies suggest that diabetes is an independent risk factor for cognitive decline and dementia. The pattern of neuropsychological performance observed in type 2 diabetic patients appears to be the result of multiple interacting processes developing over time. In addition to the detrimental effects of protracted impaired glucose regulation on the central nervous system, type 2 diabetes pathology also encompasses the detrimental effects of associated complications such as cerebrovascular disease, which is likely the main cause of the observed processing speed/reaction time decrements.

Human cortical rhythms during visual delayed choice reaction time tasks

Neuroimaging cognitive study of aging requires simple tasks ensuring a high rate of correct performances even in stressful neurophysiological settings. Here two simple delayed choice reaction time tasks were used to unveil event-related desynchronization (ERD) of theta (4-6 Hz) and alpha (6-12 Hz) electroencephalographic rhythms across normal aging. In the first condition, a cue stimulus (one bit) was memorized along a brief delay period (3.5-5.5 s). The explicit demand was visuo-spatial, but the retention could be also based on phonological and somatomotor coding. In the second condition, the cue stimulus remained available along the delay period. Correct performances were higher than 95% in both groups and tasks, although they were significantly better in young than elderly subjects (P < 0.03). During the delay period, theta and alpha ERD accompanying correct responses were recognized in the two groups, the alpha ERD being stronger and prolonged during the memory than non-memory task. On the other hand, the fronto-parietal theta and parietal alpha ERD were stronger in young than elderly subjects during both tasks. Notably, the frontal alpha ERD was negligible in elderly subjects. In conclusion, the present simple tasks unveiled in elderly compared to young subjects (i) a weaker involvement of (para)hippocampal-cortical circuits as revealed by theta ERD and (ii) a weaker involvement of "executive" thalamo-cortical circuits as revealed by frontal alpha ERD. These effects might worsen behavioral performances to the simple cognitive tasks with age. The present protocol is promising for the neuroimaging study of pathological aging.

Evaluation of the French version of EUROQUEST: a questionnaire for neurotoxic symptoms

BACKGROUND

EUROQUEST was designed to explore various neuropsychiatric symptoms caused by neurotoxic agents in occupational epidemiological studies. This paper was aimed at assessing (i) the internal consistency of the French version of EUROQUEST, (ii) its sensitivity to age, educational level and exposure, (iii) and its convergent validity by examining relationships between declared symptoms and results from psychometric tests on the same mental functions.

DESIGN

Data from four cross-sectional studies were selected: 180 workers exposed to toluene, mixed solvents or anaesthetic gas, and 588 non-exposed ones. The internal consistency of the questionnaire was assessed by computing Cronbach's alphas. Sensitivity to age, educational level and exposure were assessed with multiple linear regression models. Relationships between EUROQUEST scores and correspondent neuropsychological tests were assessed with Pearson's correlation coefficients. The relationships between EUROQUEST domain specific scores, age and educational level were evaluated for men and women from the Reference group. Most of the analyses were performed in men and women separately.

RESULTS

The results of the Cronbach's alphas computed for each EUROQUEST domain, showed a reasonable internal consistency for the questionnaire. For both women and men, memory problems and sleep disorders increased significantly with age. A significant association between EUROQUEST scores and exposure to neurotoxic agents was found for workers exposed to anaesthetic gas only. In addition, EUROQUEST memory symptoms from the Reference population were found to be correlated with two memory neuropsychological tests, both for men and women.

CONCLUSION

Our results showed a high internal consistency and a good convergent validity on assessed domains. Moreover, they showed a significant sensitivity to age, educational level and highlighted sensitivity to anaesthetic gas exposure.

Cognitive function in community-dwelling elderly women. Attentional demands and capacity to direct attention

As individuals get older, their capacity to direct attention (CDA) appears to decline. The decline in CDA may be caused by age-related changes in the brain and demands on attentional mechanisms. These demands require older adults to expend significant attentional effort to maintain focus and achieve mental clarity while negotiating activities of daily life. The purpose of this study was to examine the relationship between attentional demands and CDA among a convenience sample of 72 community-dwelling older women with normal mental status. Findings indicate attentional demands correlated significantly with CDA and accounted for a significant proportion of the variance. No relationship was found between depressive symptoms and CDA. Implications for practice are nursing interventions aimed at decreasing attentional demands, thereby supporting attentional processes and functioning by community-dwelling older adults.

Neurophysiological signals of working memory in normal aging

To examine how neurophysiological signals of working memory (WM) change with normal aging, we recorded EEGs from healthy groups (n=10 each) of young (mean age=21 years), middle-aged (mean=47 years), and older (mean=69 years) adults. EEGs were recorded while subjects performed easy and difficult versions of a spatial WM task. Groups were matched for IQ (mean=123; WAIS-R) and practiced in task performance. Responses slowed with age, particularly in the more difficult task. Advanced age was associated with decreased amplitude and increased latency of the parietal P300 component of the event-related potential and an increase in the amplitude of a frontal P200 component. Spectral features of the EEG also differed between groups. Younger subjects displayed an increase in the frontal midline &theta; rhythm with increased task difficulty, a result not observed in older subjects. Age-related changes were also observed in the task-related alpha signal, the amplitude of which decreases as more neurons become involved in task-related processing. Young adults showed a decrease in alpha power with increased task difficulty over parietal regions but not over frontal regions. Middle-aged and older adults showed decreased alpha power with increased task difficulty over both frontal and parietal regions. This suggests that normal aging may be associated with changes in the fronto-parietal networks involved with spatial WM processes. Younger subjects appear to use a strategy that relies on parietal areas involved with spatial processing, whereas older subjects appear to use a strategy that relies more on frontal areas.

The role of sequential stream segregation and frequency selectivity in the perception of simultaneous sentences by listeners with sensorineural hearing loss

The purpose of this study was to determine the role of frequency selectivity and sequential stream segregation in the perception of simultaneous sentences by listeners with sensorineural hearing loss. Simultaneous sentence perception was tested in listeners with normal hearing and with sensorineural hearing loss using sentence pairs consisting of one sentence spoken by a male talker and one sentence spoken by a female talker. Listeners were asked to repeat both sentences and were scored on the number of words repeated correctly in each sentence. Separate scores were obtained for the first and second sentences repeated. Frequency selectivity was assessed using a notched-noise method in which thresholds for a 1,000 Hz pure-tone signal were measured in noise with spectral notch bandwidths of 0, 300, and 600 Hz. Sequential stream segregation was measured using tone sequences consisting of a fixed frequency (A) and a varying frequency tone (B). Tone sequences were presented in an ABA_ABA_... pattern starting at a frequency (B) either below or above the frequency of the fixed 1,000 Hz tone (A). Initially, the frequency difference was large and was gradually decreased until listeners indicated that they could no longer perceptually separate the two tones (fusion threshold). Scores for the first sentence repeated decreased significantly with increasing age. There was a strong relationship between fusion threshold and simultaneous sentence perception, which remained even after partialling out the effects of age. Smaller frequency differences at fusion thresholds were associated with higher sentence scores. There was no relationship between frequency selectivity and simultaneous sentence perception. Results suggest that the abilities to perceptually separate pitch patterns and separate sentences spoken simultaneously by different talkers are mediated by the same underlying perceptual and/or cognitive factors.

Age-related metabolite changes and volume loss in the hippocampus by magnetic resonance spectroscopy and imaging

Magnetic resonance imaging (MRI) studies have produced controversial results concerning the correlation of hippocampal volume loss with increasing age. The goals in this study were: 1) to test whether levels of N-acetyl aspartate (NAA, a neuron marker) change in the hippocampus during normal aging and 2) to determine the relationship between hippocampal NAA and volume changes. Proton magnetic resonance spectroscopic imaging (1H MRSI) and MRI were used to measure hippocampal metabolites and volumes in 24 healthy adults from 36 to 85 years of age. NAA/Cho decreased by 24% (r = 0.53, p = 0.01) and NAA/Cr by 26% (r = 0.61, p < 0.005) over the age range studied, whereas Cho/Cr remained stable, implying diminished NAA levels. Hippocampal volume shrank by 20% (r = 0.64, p < 0.05). In summary, aging effects must be considered in 1H MRSI brain studies. Furthermore, because NAA is considered a marker of neurons, these results provide stronger support for neuron loss in the aging hippocampus than volume measurements by MRI alone.