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Biomedical subjects

G E Alexander

Publications and source records attributed to G E Alexander.

89 records · Page 5Linked to original sources
PubMed1982

Necrotizing arteritis and spinal subarachnoid hemorrhage in Sjögren syndrome.

A 37-year-old woman with primary Sjögren syndrome developed mixed cryoglobulinemia and systemic vasculitis. Subarachnoid hemorrhage occurred as a result of necrotizing anterior spinal arteritis. Although rarely seen in mixed cryoglobulinemia, central nervous system complications have recently been documented in Sjögren syndrome. The patient's serum contained antibodies to the Ro(SSA) cytoplasmic antigen, and these antibodies were concentrated in the cryoglobulin fraction. Anti-Ro(SSA) antibodies are associated with the occurrence of vasculitis in patients with Sjögren syndrome, which suggests that the spinal arteritis and subarachnoid hemorrhage in this patient may have been directly related to the underlying connective tissue disorder.

Adult↗
PubMed1982

Neurologic complications of primary Sjögren's syndrome.

Although peripheral nervous system disease has been well documented in Sjögren's syndrome (SS), central nervous system (CNS) involvement is considered distinctly uncommon. Sixteen patients with primary SS and CNS disorders not attributable to other causes were the subjects of this study. Cerebral manifestations, both focal and diffuse, as well as spinal cord disease, were observed. Peripheral vasculitis occurred in 12 patients (75%), 83% of whom had anti-Ro(SSA) antibodies. The high proportion of patients with concomitant peripheral vasculitis, and the observed association with antibodies to the Ro(SSA) antigen system which, in other studies, has been linked to vasculitis in SS, suggest that an immune vasculopathy may play a role in the pathogenesis of the CNS disease of SS.

Adult↗
PubMed1981

Sjögren syndrome: central nervous system manifestations.

We studied eight patients who had primary Sjögren syndrome and central nervous system (CNS) disorders that were not attributable to other causes. Focal cerebral deficits were observed in five patients. Aseptic meningoencephalitis was seen in five patients, recurrent in one. Spinal cord manifestations in three patients took several forms: acute transverse myelitis, chronic progressive myelopathy, and spinal subarachnoid hemorrhage. Precipitating antibodies to the Ro(SSA) cytoplasmic antigen were detected in the sera of seven of eight patients. This may be relevant to the pathogenesis of CNS disease in Sjögren syndrome, because there is a strong correlation between vasculitis and the presence of anti-Ro(SSA) antibodies in this connective tissue disorder.

Adult↗
PubMed1980

Neural processing of vocalizations and artificial stimuli in the medial geniculate body of squirrel monkey.

The responses of 256 single neurons in the medial geniculate body of awake squirrel monkeys have been examined with a variety of acoustic stimuli. Both traditional artificial sounds and tape-recorded tokens of species-specific vocalizations were employed, and one goal of the study was the comparison along a number of response parameters of these two classes. Unit responses to the first group (clicks, tone bursts and noise bursts) revealed a level of responsivity approaching 100% in the principal nucleus. Responses to tone and noise were sustained in about half the cells, and characteristic frequencies could be identified in 81%. Responses to vocal stimuli were also very prevalent, approaching 100% in this sample. A comparison of absolute thresholds, response vigor, rate-level functions, binaural interactions, and spectral composition of effective stimuli confirmed that MGB cells process vocal stimuli and artificial stimuli in similar ways. Selectivity of MGB cells to vocal stimuli was quite low, suggesting that processing of communication sounds in MGB is relatively simple and preliminary when compared to auditory cortex.

Acoustic Stimulation↗
PubMed1978

Functional development of the dorsolateral prefrontal cortex: an analysis utlizing reversible cryogenic depression.

The dorsolateral prefrontal cortex of rhesus monkeys was functionally inactivated by local hypothermia as the monkeys performed spatial delayed-response and spatial delayed-alternation tasks at different stages of postnatal development. Cryogenic depression of prefrontal cortex at a temperature sufficient to induce 21--25% decrements in delayed-response performance in 34--36-month-old-monkeys, produced deficits of only 7--8% in 19--31-month-old and no detectable loss in younger monkeys, 9--16 months of age. Delayed-alternation performance was impaired by local hypothermia as early as 8.5 months of age, but maximal cooling-induced deficits on this task were not observed before 33 months of age. Thermal gradients mapped in representative monkeys at different stages of development were remarkable similar, indicating that the age-dependent differences in behavior were not attributable to technical factors. The results obtained in the present study on normal developing monkeys confirm the interpretation of previous research on brain-damaged infants that functional maturation of the dorsolateral prefrontal cortex is protracted over several years of postnatal life, and extends the earlier studies by indicating that the lower limit for maturity of dorsolateral function is close to puberty in this species. Further, the present study revealed that delayed-response and delayed-alternation performance are dissociable dorsolateral functions which achieve maturity at different rates. The convergence of evidence from reversible neural depression and permanent lesion methods provides strong validation for neurobehavioral analysis as a general approach to the study of regional maturation of the brain.

Age Factors↗
PubMed1971

Neuron activity related to short-term memory.

Nerve cells in the monkey's prefrontal cortex and nucleus medialis dorsalis of the thalamus show changes of firing frequency associated with the performance of a delayed response test. Most cells increase firing during the cue presentation period or at the beginning of the ensuing delay; spike discharge highler than that in intertrial periods is present in some cells throughout the delay. These changes are interpreted as suggestive evidence of a role of frontothalamic circuits in the attentive process involved in short-term memory

Action Potentials↗
PubMedDate not supplied

Age-related differences in visual perception: a PET study.

To assess age-related differences in cortical activation during form perception, two classes of visual textures were shown to young and older subjects undergoing positron emission tomography (PET). Subjects viewed even textures that were rich in rectangular blocks and extended contours and random textures that lacked these organized form elements. Within-group significant increases in regional cerebral blood flow (rCBF) during even stimulation relative to random stimulation in young subjects were seen in occipital, inferior and medial temporal regions, and cerebellum, and in older subjects, in posterior occipital and frontal regions. Group by texture type interactions revealed significantly smaller rCBF increases in older subjects relative to young in occipital and medial temporal regions. These results indicate that young subjects activate the occipitotemporal pathway during form perception, whereas older subjects activate occipital and frontal regions. The between-group differences suggest that age-related reorganization of cortical activation occur during early visual processes in humans.

Adult↗
PubMedDate not supplied

Regional pattern of hippocampus and corpus callosum atrophy in Alzheimer's disease in relation to dementia severity: evidence for early neocortical degeneration.

We used volumetric MRI and analysis of areas under receiver operating characteristic (ROC) curves to directly compare the extent of hippocampus-amygdala formation (HAF) and corpus callosum atrophy in patients with Alzheimer's disease (AD) in different clinical stages of dementia. Based on neuropathological studies, we hypothesized that HAF atrophy, representing allocortical neuronal degeneration, would precede atrophy of corpus callosum, representing loss of neocortical association neurons, in early AD. HAF and corpus callosum sizes were significantly reduced in 27 AD patients (37% and 16%, respectively) compared to 28 healthy controls. In mildly- and moderately-demented AD patients, the ROC derived index of atrophy was greater for HAF volume than for total corpus callosum area. The index of atrophy of posterior corpus callosum was not significantly different from HAF at mild, moderate or severe stages of dementia. In conclusion, these findings suggest a characteristic regional pattern of allocortical and neocortical neurodegeneraton in AD. Our data indicate that neuronal loss in parietotemporal cortex (represented by atrophy of corpus callosum splenium) may occur simultaneously with allocortical neurodegeneration in mild AD. Moreover, ROC analysis may provide a statistical framework to determine atrophy patterns of different brain structures in neurodegenerative diseases in vivo.

Aged↗
PubMedDate not supplied

PET reveals occipitotemporal pathway activation during elementary form perception in humans.

To define brain regions involved in feature extraction or elementary form perception, regional cerebral blood flow (rCBF) was measured using positron emission tomography (PET) in subjects viewing two classes of achromatic textures. Textures composed of local features (e.g. extended contours and rectangular blocks) produced activation or increased rCBF along the occipitotemporal pathway relative to textures with the same mean luminance, contrast, and spatial-frequency content but lacking organized form elements or local features. Significant activation was observed in striate, extrastriate, lingual, and fusiform cortices as well as the hippocampus and brain stem. On a scan-by-scan basis, increases in rCBF shifted from the occipitotemporal visual cortices to medial temporal (hippocampus) and frontal lobes with increased exposure to only those textures containing local features. These results suggest that local feature extraction occurs throughout the occipitotemporal (ventral) pathway during extended exposure to visually salient stimuli, and may indicate the presence of similar receptive-field mechanisms in both occipital and temporal visual areas of the human brain.

Adult↗