Calcium metabolism appears to underlie neuronal cell death via excitotoxicity,     and hormonally active vitamin D confers a protective effect in vitro at physiologically relevant concentrations up to 100nM but not above.  This mechanism of protection appears to be mediated via a downregulation of L-type voltage-sensitive Ca 2+ ion channels,  an effect which has also been seen in bone cells.   These L-type channels have been implicated in excitotoxicity.  
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The attention impairments in MHE are observed on a variety of measures. These include measures of cognitive processing speed involving psychomotor responding, such as the Number Connection tests (NCT), block design test (BDT),the Digit Symbol test (DST), line drawing test, circle-dotting test, serial-dotting test, figure connection test. Impairments on measures of cognitive processing speed and response inhibition that do not require a motor response have also been reported (., with verbal fluency tasks and measures such Stroop test). 22,23 Visuospatial impairments have been primarily reported on block design tasks (which also include a motor/practic component), but also on more pure measures of visuospatial perception, such as line orientation or the Hooper test. Fine motor skill impairments have been noted on measures such as the grooved pegboard task, and on line tracing tasks (the latter also involve visuospatial abilities). 24