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John C Adair

Publications and source records attributed to John C Adair.

11 recordsLinked to original sources
PubMed2006

Aging: compensation or maturation?

Neuroimaging studies of healthy aging often reveal differences in neural activation patterns between young and elderly groups for episodic memory tasks, even though there are no differences in behavioral performance. One explanation typically offered is that the elderly compensate for their memory deficiencies through the recruitment of additional prefrontal regions. The present study of healthy aging compared magnetoencephalographic (MEG) time-courses localized to specific cortical regions in two groups of subjects (20-29 years and >or=65 years) during a visual delayed-match-to-sample (DMS) task. MR morphometrics and neuropsychological test results were also examined with the hope of providing insight into the nature of the age-related differences. The behavioral results indicated no differences in performance between young and elderly groups. Although there was a main effect of age on the latency of the initial peak in primary/secondary visual cortex, these longer latencies were not correlated with the performance of elderly on the DMS task. The lateral occipital gyrus (LOG) revealed qualitatively different patterns of activity for the two age groups corroborated by neuropsychological test results. Morphometric results for the young versus elderly groups revealed less white (WM) and gray matter (GM) volumes in the frontal lobes of the elderly. When a group of middle-aged subjects (33-43 years) was included in the morphometric analyses, the middle-aged subjects revealed statistically greater WM volumes in frontal and parietal cortex suggesting immature WM tracts in the young. Perhaps our elderly utilized a different strategy compared to the young due to the different brain maturation levels of these groups.

Adult↗
PubMed2006

The neural networks underlying endogenous auditory covert orienting and reorienting.

Auditory information communicated through vocalizations, music, or sounds in the environment is commonly used to orient and direct attention to different locations in extrapersonal space. The neural networks subserving attention to auditory space remain poorly understood in comparison to our knowledge about attention in the visual system. The present study investigated whether a parietal-prefrontal right-hemisphere network controls endogenous orienting and reorienting of attention to the location of sounds just as it does for visual-spatial information. Seventeen healthy adults underwent event-related functional magnetic resonance imaging (FMRI) while performing an endogenous auditory orienting task, in which peripheral cues correctly (valid) or incorrectly (invalid) specified the location of a forthcoming sound. The results showed that a right precuneus and bilateral temporal-frontal network mediated the reorienting of auditory attention at both short and long stimulus onset asynchronies (SOAs). In contrast, the more automatic stage of auditory reorienting at the shorter SOA was associated with activation in a bilateral inferior parietal-frontal oculomotor network. These findings suggest that the reorienting of auditory attention is generally supported by a similar inferior parietal-frontal network as visual attention, but in both hemispheres. However, peripheral auditory cues also appear to elicit an automatic orienting response to the spatial location of a sound followed by a period of reduced processing of information that occurs in the same location later in time.

Adult↗
PubMed2005

Age-related effects on superior temporal gyrus activity during an auditory oddball task.

We used magnetoencephalography in combination with magnetic resonance imaging to investigate the effects of aging on the temporal dynamics of activity localized to several brain regions during an auditory oddball task. The most interesting effects were noted in the superior temporal gyrus as follows: (1) responses were generally stronger to rare than to frequent tones throughout the entire 600-ms time interval, and (2) increases in the amplitude of the 40-ms peak and the latency of the maximum late response were evident in the elderly. Although superior temporal gyrus activity has traditionally been associated with early sensory processing, these results suggest that superior temporal gyrus activity is also important for later decision-related processing.

Acoustic Stimulation↗
PubMed2005

Temporal dynamics of age-related differences in auditory incidental verbal learning.

Auditory response profiles for a group of ten healthy young and ten healthy elderly subjects, evoked by implicit memory and delayed verbal recognition tasks, were evaluated to determine if effects of stimulus repetition could be identified in the superior temporal gyrus (STG) and prefrontal cortical regions. We hypothesized that effects of stimulus repetition should occur both early in time and at early levels of the nervous system (STG) followed by later effects in prefrontal regions. Magnetoencephalographic (MEG) responses were recorded using a whole-head MEG system and automated, multi-start analysis methods were applied to the data in order to characterize the temporal response profiles from distributed but focal, cortical regions engaged in memory-related tasks. The findings revealed a main effect of age for early activity ( approximately 50 ms) in STG which appeared to be nonspecific for Old/New words and an Age x Task interaction for late activity ( approximately 100-800 ms) in STG which was specific to Old/New words. Although the behavioral performance measures did not reveal traditional effects of response priming, the MEG measures did reveal a reduction in amplitude with stimulus repetition in young subjects. The elderly did not reveal a reduction in amplitude concomitant with stimulus repetition for either the global attributes of words or for specific Old/New words. Long duration effects of stimulus repetition noted in the present study raise the possibility that results from sensory gating, mismatch negativity and P300 paradigms may represent a continuum of stimulus repetition effects. Two of these paradigms evoke greater enhancement to novel or infrequent stimuli, or rather, greater reduction of amplitude with repetition.

Adult↗
PubMed2004

Measurement of gelatinase B (MMP-9) in the cerebrospinal fluid of patients with vascular dementia and Alzheimer disease.

BACKGROUND AND PURPOSE: Vascular causes of dementia are increasing in importance because of the aging of the population. Biological markers to distinguish patients with vascular dementia (VaD) from Alzheimer disease (AD) would be very useful. Because cerebrovascular disease increases expression of brain matrix metalloproteinases (MMPs) and tissue inhibitors to metalloproteinases (TIMPs), we hypothesized that MMPs would be elevated in the cerebrospinal fluid (CSF) of patients with VaD, but not in patients with AD. METHODS: Fifteen patients with VaD were identified, including dementia caused by multiple infarcts and progressive dementia caused by disease of the small cerebral blood vessels. Patients were followed-up for 4 to 10 years to confirm the diagnosis. Thirty patients with AD were also studied. Patients had CSF collected at their initial evaluation. Gelatinase A (MMP-2) and gelatinase B (MMP-9) were quantified by gelatin-substrate zymography, and TIMPs were measured by reverse zymography. Control CSF was obtained from neurologically normal subjects. RESULTS: MMP-9 levels were significantly elevated in the CSF of VaD patients compared either to those with AD (P<0.0001) or to controls. MMP-2, TIMP-1, and TIMP-2 were similar in patient groups and controls. CONCLUSIONS: Patients with multiinfarct and small vessel VaD have elevated levels of MMP-9 in the CSF compared with AD and controls. Although CSF MMP-9 increases in other neurological conditions and is not specific for VaD, it could provide an additional biological marker for the separation of patients with VaD and AD.

Alzheimer Disease↗
PubMed2004

Visual search pattern during the line quadrisection task in normal subjects.

A common test for the assessment of hemispatial neglect is the line bisection test. A recent modification of the task has been reported wherein subjects place a mark at either 25% or 75% of line length ('quadrisection'). In a previous study, we suggested that line quadrisection might entail iteration of two steps involved in standard line bisection: (1) finding the midpoint of the entire line, and then (2) bisecting the half-line segment between the adjudged midpoint and the line end ipsilateral to the target quadrisection point. The present study investigated eye movement patterns during line quadrisection in order to test this hypothesis. Twenty normal volunteers determined the left or right quadrisection point of a horizontal line while their eye movements were recorded using two-dimensional video-oculography. Analysis revealed that, like the results of previous studies on bisection, most normal subjects fixate the central portion of the line segment before reaching the target area during the quadrisection task. Normal subjects' eye movements during quadrisection performance share a number of features with line bisection and provide support for the two-step processing hypothesis.

Adult↗
PubMed2004

Pseudoneglect in solid-line versus character-line bisection tasks: a test for attention dominance theory.

OBJECTIVE: Normal subjects tend to bisect lines slightly to the left of the true midpoint, a phenomenon termed pseudoneglect. To test whether pseudoneglect relates to the right hemisphere's dominance for spatial attention or to the hemispheric difference in processing global-local stimulus properties, we administered conventional solid-line (SBT) and novel character-line (CBT) bisection tasks to normal subjects of different ages. METHODS: Normal subjects, consisting of 40 young and 40 older individuals, received 3 experimental tasks, a standard SBT and 2 types of CBT. Each subject completed 10 consecutive trials of each task presented in counterbalanced order between subjects. RESULTS: Across age groups, deviations on CBT were further to the right than those of SBT, and the leftward bias (pseudoneglect) was significant only in SBT. CONCLUSION: These results indicate that the bisection errors in normal subjects depend on the characteristics demanded by the specific task. Thus, our findings argue against the attention dominance theory and support a "task specificity" theory for pseudoneglect.

Adult↗
PubMed2003

Caloric stimulation in neglect: evaluation of response as a function of neglect type.

Contralesional neglect may be induced by either unawareness of contralesional stimuli (attentional neglect, AN) or failure to act in contralesional space (intentional neglect, IN). We examined whether contralesional cold caloric stimulation differentially affects AN versus IN. Patients with left-sided neglect (n = 16) from right-hemisphere lesions performed target cancellation and line bisection tasks. Using a video-based apparatus that reverses the right and left side of stimuli, patients with abnormal cancellation performance were divided into those with AN and those with IN. The 5 subjects with normal cancellation performance but rightward bisection bias were also separated into 2 neglect groups. Subjects performed cancellation or bisection tasks before and immediately after irrigation of the left auditory canal with ice water. Caloric stimulation induced brisk rightward nystagmus in all subjects. Subjects with AN cancelled more left-sided targets after stimulation than those with IN (p = .02). Whereas caloric stimulation significantly shifted bisection error leftward for both IN and AN groups (p < .0001), AN patients exhibited a greater magnitude of shift than the IN patients. While the basis for differential performance remains undefined, the data indicate that caloric stimulation influences AN more than IN.

Aged↗
PubMed2002

Effect of background motion on line bisection performance in normal subjects.

Previous studies have demonstrated that optokinetic stimulation (OKS) influences line bisection (LB) performance in normal subjects and patients with hemispatial neglect. Since subjects were required to attend to stationary targets on a moving background, prior experimental designs might have induced an illusion of target motion or induced motion (IM) in a direction opposite the background. The current study tested whether the IM affects LB performance in normal subjects and how the speed of targets also influences LB. Thirty-two right-handed normal volunteers (aged 28.0 +/- 5.3 years) were asked to bisect stationary lines with a background of horizontal OKS. These stimuli were generated by computer displayed on a large screen via a beam projector. The OKS was varied according to direction (leftward or rightward) and speed (9.4 degrees/sec or 56.1 degrees/sec), producing 4 different experimental conditions. Mean bisection errors in all conditions were compared with a control condition with no background OKS. For each condition, subjects rated the degree of IM on a 5 point scale. With fast rate OKS, subjects reported minimal IM and LB errors were in the same direction as background motion, a finding that replicates previous studies. Conversely, the slow OKS rate caused subjects to report IM and resulted in deviation of the bisection mark in a direction opposite the background OKS. While this discrepancy between the slow and fast OKS conditions might be related to motion illusion, we did not find a direct correlation between the degree of IM and bisection errors and thus reasons for these results remain unexplained.

Adult↗
PubMed2002

Neuropsychiatric systemic lupus erythematosus presenting as amyotrophic lateral sclerosis.

A 61-year-old woman with a history of photosensitive dermatitis and recurrent mouth ulcers presented with progressive weakness typical of amyotrophic lateral sclerosis (ALS), and subsequently underwent extensive neurologic and rheumatologic testing. We investigated whether ALS-like motor neuron disease associated with a positive antinuclear antibody (ANA) is really ALS or rather neuropsychiatric systemic lupus erythematosus (NPSLE). On neurologic evaluation, she had prominent bulbar involvement with dysarthria and dysphagia associated with profound lingual fasciculations and a denervating pattern on electromyogram. MRI showed no evidence of cerebral ischemia. Laboratory studies revealed a positive ANA (1:2560 titer), positive antiphospholipid antibodies (GPL and MPL), circulating lupus anticoagulant, and depressed C3 and C4. Repeat MRI studies at 4 and 11 mo revealed an evolving infarct in the paramedian pons consistent with the presence of NPSLE. Therapy was initiated with corticosteroids and intravenous cyclophosphamide, and the neurologic condition did not improve, but also did not progress inexorably as would be expected with ALS. NPSLE, presumably through the mechanism of ischemic vasculopathy, may present as motor neuron disease clinically indistinguishable from ALS.

Amyotrophic Lateral Sclerosis↗