610 Neurocognitive Disorders
and symptoms more subtle. Ideally, individu als will be referred for formal neuropsycho-
logical testing, which will provide a quantitative assessment of all relevant domains and
thus help with diagnosis; provide guidance to the family on areas where the individual
may require more support; and serve as a be nchmark for further decline or response to
therapies. When such testing is  unavailable or not feasible, the brief assessments in Table 1
can provide insight into each domain. More glob al brief mental status tests may be helpful
but may be insensitive, particul arly to modest changes in a single domain or in those with
high premorbid abilities, and may be overly sensitive in those with low premorbid abilities.
In distinguishing among etiological subtypes, additional diagnostic markers may
come into play, particularly neuroimaging studies such as magnetic resonance imaging
scans and positron emission tomography scans. In addition, specific markers may be in-
volved in the assessment of specific subtypes  and may become more important as addi-
tional research findings accumulate over time, as discussed in the relevant sections. 
Functional Consequences of 
Major and Mild Neurocognitive Disorders 
By definition, major and mild NCDs affect func tioning, given the central role of cognition in
human life. Thus, the criteria for the disorder s, and the threshold for differentiating mild
from major NCD, are based in part on functi onal assessment. Within major NCD there is a
broad range of functional impairment, as implem ented in the severity specifiers. In addition,
the specific functions that are compromised can help identify the cognitive domains affected,
particularly when neuropsychological testing is  not available or is difficult to interpret. 
Differential Diagnosis
Normal cognition. The differential diagnosis between  normal cognition and mild NCD,