Morphologic characteristics of physiologically defined neurons in the cat trigeminal nucleus principalis.

Although the principalis nucleus (Vp) contains trigeminothalamic and internuclear tract cells, the functional and morphologic differences between the two kinds of neurons have remained unsettled. The present study was aimed to address these problems by using the intracellular horseradish peroxidase injection technique in the cat. Of 20 neurons stained, 7 and 13 were located in the dorsomedial subnucleus (Vpd) and ventrolateral subnucleus (Vpv) of Vp, respectively. The Vpd neurons received input from the intraoral structures only but the Vpv neurons from the intraoral or facial structures. Nineteen neurons could be divided as class I and class II, based on the branching pattern of their stem axons. Class I (eight neurons) had an ascending stem axon without branching. Class II was divided into two subclasses (IIa and IIb). Class IIa (eight neurons) had an ascending stem axon from which branches were given off. Their branches formed a local-circuit restricted to the lower brainstem. Class IIb (three neurons) had a stem axon that formed the local-circuit only. The dendritic morphology was indistinguishable between different classes of neurons and between the subdivisions. Although the dendritic arborization pattern was governed by the location of the somata, it was suggested to be also important elements for determining primary afferent arborizations. In the brainstem nuclei, the jaw-closing motor nucleus received the highest density of projections from class II neurons with the receptive field involving the periodontal ligaments. The present study provides new findings that Vp neurons could be divided into three distinct populations and suggests that each population exerts a distinct function with respect to sensory discrimination, sensorimotor reflexes, or both.

Age at onset and language disturbances in Alzheimer's disease.

This study examined the effect of age at symptom onset of Alzheimer's disease (AD) on the pattern of language disturbance. We assessed 150 consecutive patients with a clinical diagnosis of mild-to-moderate AD using the Western Aphasia Battery and a 100-item picture-naming test. A multivariate linear regression analysis examined the effect of age at onset after controlling for gender, education, severity of dementia and duration of the disease. Patients with early onset performed significantly worse than did patients with late onset on the word comprehension and sequential commands subtests. On the other hand, late-onset patients performed more poorly than early-onset patients on the picture-naming test in a subgroup with mild language deficits. However, the trend disappeared in other subgroups with more degraded language function. We consider that the concomitant effects of normal aging worsened the picture-naming deficits in the late-onset patients, and the rapid decline of naming ability in the early-onset patients masked the aging effect with the progression of language deficits. The deterioration of word comprehension and the rapid decline of naming ability are the characteristics of early-onset patients. The different patterns of language deficits between early- and late-onset patients may correspond to the genetic heterogeneity of AD.

Functional properties of the primary motor cortex and ventral premotor cortex in the monkey during a visually guided jaw-movement task with a delay period.

This study investigated single neuronal activity in the face area of the primary motor cortex (MI) and ventral part of the premotor cortex (PMv) while a monkey performed a visually guided jaw-movement task with a delay period. When the monkey executed the jaw movements, 48 MI and 53 PMv neurons showed statistically significant activities time-locked to jaw movements and were defined as movement-related neurons. The activities of movement-related neurons could be classified into phasic, phasic-tonic and tonic patterns based on the changes in discharge rate. Most of the neurons exhibiting phasic and phasic-tonic activities probably contributed to the initiation of jaw movements, since they exhibited transient responses immediately after the onset of the go-cue indicating the jaw movement. In contrast, the sustained activity of the movement-related neurons exhibiting phasic-tonic and tonic activities may be involved in controlling and/or maintaining jaw position. Sustained activity was also detected during the delay period in 4 MI and 29 PMv neurons and these neurons were defined as set-related neurons. It is thought that these set-related neurons are involved in the preparation for the subsequent jaw movement, since the masticatory muscles showed no significant changes during the delay period. These findings suggest that the MI may be involved predominantly in the initiation and control of jaw movements, and that the PMv may be involved in motor preparation, and may play a role as a higher-order motor area related to the initiation and control of jaw movements.

Morphology and Physiology of the Thoracic and Abdominal Stretch Receptors of the Isopod Crustacean Ligia exotica.

In the terrestrial isopod Ligia exotica, paired stretch receptors, each comprising a separate rapidly and slowly adapting receptor cell, were found in the third to eighth thoracic segments and first five abdominal segments. The dendritic endings of the two sensory cells in each receptor terminate on a common receptor muscle; the cross-striation of this fiber is homogeneous throughout the segments. But the dendritic endings of the receptor cells differ: the rapidly adapting cell has a club-shaped ending restricted to the middle of the receptor muscle, whereas the slowly adapting receptor cell has a bifurcating ending that extends along the entire length of the muscle. Stretch applied to the receptor muscle evokes characteristically different responses in the two sensory cells. The slowly adapting receptor cell has a lower firing threshold and fires continuously for the duration of the stretch, while the rapidly adapting receptor cell has a higher threshold and fires a brief burst at the beginning of the stimulus. However, application of an intense stimulus will evoke continuous firing of the rapidly adapting receptor, which then changes to intermittent bursts. The adaptive significance of such a response is not known, nor is it likely to occur in nature. However, this unusual response is intrinsic to the rapidly adapting cell, as it can be evoked by current injection. In the second thoracic segment, instead of rapidly and slowly adapting cells, we found a single slowly adapting cell with a long robust dendrite attached to the extensor muscle.

Hereditary sensory neuropathy with deafness and dementia: a clinical and neuroimaging study.

We describe three sibling patients with autosomal dominantly inherited sensory neuropathy, sensorineural hearing loss and dementia. The features of cognitive-behavioral deficits in the patients, including executive dysfunction, apathy, indifference and inattention, were consistent with a frontal lobe dysfunction. Magnetic resonance imaging showed a diffuse brain atrophy. A fluorodeoxyglucose positron emission tomography in one patient and a single photon emission computed tomography in another demonstrated a glucose hypometabolism or a hypoperfusion in the medial frontal and thalamic regions. Primary frontal involvement or frontal dysfunction secondary to thalamic lesions may contribute to the nature of dementia in these patients.

Procedural memory in patients with mild Alzheimer's disease.

Motor, perceptual, and cognitive skill learning abilities of mild Alzheimer's disease (AD) patients were compared to sex-, age-, and education-matched controls. We excluded patients who were unable to perform each skill learning task with a predetermined criterion. In those who completed the task, skill learning was as good as in normal controls. On the cognitive and perceptual skill learnings, some of the AD patients, whose cognitive but not declarative memory functions were more severely impaired than in those who completed the whole session, failed to complete the task, while all patients could complete the motor task. These results support that view that patients with mild AD can acquire motor, perceptual, and cognitive skills and that the neural system subserving procedural skill is not related to the neural systems for declarative memory.

Neuronal substrates for semantic memory: a positron emission tomography study in Alzheimer's disease.

We examined 57 patients with mild Alzheimer's disease by using three kinds of verbal semantic memory tests (category fluency, confrontation naming and generation of verbal definition) and correlated each score with regional cerebral glucose metabolism determined by (18)F-fluorodeoxyglucose and positron emission tomography. The scores of all three verbal semantic memory tests correlated significantly with regional cerebral glucose metabolism in the left inferior temporal gyrus, even after controlling for the effects of age, sex and educational attainment. In contrast, the scores of the word recall test did not correlate significantly with regional cerebral glucose metaboliosm in the left inferior temporal gyrus, neither before nor after controlling for these confounders. Our results suggested that the left inferior temporal lobe contributes to verbal semantic memory.

Regional hypometabolism related to language disturbance in Alzheimer's disease.

To elucidate the nature of language disturbance in Alzheimer's disease (AD) and the cerebral area involved in it, we studied 65 AD patients with the Western Aphasia Battery (WAB) and with 18F-fluorodeoxyglucose and positron emission tomography. Partial correlations were evaluated between the Aphasia Quotient of WAB and regional cerebral glucose metabolism normalized by the mean metabolic rate in the bilateral primary sensorimotor areas after controlling age, sex, education and severity of illness. Language disturbance in AD is accounted for by deficits in the semantic processing of language and is related to glucose hypometabolism in the inferior temporal gyrus and inferior parietal lobule, especially in the dominant side. These results offer further evidence suggesting that the lexico-semantic processing system is mediated in these regions.