Adult alpha-mannosidosis: clinical progression in the absence of demyelination.

Alpha-mannosidosis is an inherited lysosomal storage disease. The authors report three siblings (ages 38 to 47 years) with the rare adult variant. All three had late-onset ataxia and retinal degeneration, adding to hearing loss, cognitive impairment, and dysotosis multiplex. One sibling also had psychosis. MRI revealed cerebellar atrophy and predominantly parieto-occipital white matter changes. MR spectroscopy showed no evidence for demyelination. It appears that the disabling course of adult alpha-mannosidosis is caused by lysosomal accumulation rather than demyelination.

Fast temporal interactions in human auditory cortex.

The temporal resolution of the human primary auditory cortex (AC) was studied using middle-latency evoked fields. Paired sounds with either the same or different spectral characteristics were presented with gaps between the sounds of 1, 4, 8 and 14 ms. Spatio-temporal modelling showed (1) that the response to the second sound was recognizable with gaps of 1 ms and rapidly increased in amplitude with increasing gap durations, (2) an enhanced N40m amplitude at gaps > 4 ms, (3) delayed N19m-P30m latencies when the stimuli were different. The median psychoacoustical thresholds were 1.6 ms for the same stimuli and 2.5 ms for different stimuli, confirming the electrophysiological evidence for rapid pattern-specific temporal processing in human primary auditory cortex.

Deconvolution of 40 Hz steady-state fields reveals two overlapping source activities of the human auditory cortex.

Steady-state auditory evoked fields were recorded from 15 subjects using a whole head MEG system. Stimuli were 800 ms trains of binaural clicks with constant stimulus onset asynchrony (SOA). Seven different SOA settings (19, 21, 23, 25, 27, 29 and 31 ms) were used to give click rates near 40 Hz. Transient responses to each click were reconstructed using a new algorithm that deconvoluted the averaged responses to the different trains. Spatio-temporal multiple dipole modelling in relation to 3D MRI scans revealed two overlapping source components in both the left and right auditory cortex. The primary sources in the medial part of Heschl's gyrus exhibited a N19-P30-N40 m pattern. The secondary, weaker sources at more lateral sites on Heschl's gyrus showed a N24-P36-N46 m pattern. When applied to transient middle latency auditory evoked fields (MAEFs) recorded at SOAs of 95-135 ms, the primary sources imaged activities similar to the deconvoluted steady-state responses, but the secondary source activities were inconsistent. Linear summation of the deconvoluted source waveforms accounted for more than 96% of the steady-state variance. This indicates that the primary activity of the auditory cortex remains constant up to high stimulation rates and is not specifically enhanced around 40 Hz.