A cognitive electrophysiological signature differentiates amnestic mild cognitive impairment from normal aging

Participants

Participants were 18 NC (7 male, 11 female) between the ages of 67 and 83 years (mean?=?75.11, SD?=?4.95), 16 with aMCI (11 male, 5 female) between the ages of 62 and 90 years (mean?=?75.31, SD?=?9.21), and 13 patients with AD (5 male, 8 female) between the ages of 66 and 82 years (mean?=?75.77, SD?=?5.67). The three groups did not differ in age [F(2,46)?=?0.035, p?=?0.97], sex distribution [?²(2)?=?3.73, p?=?0.16], or years of education (NC group mean =16.22, SD?=?3.02; aMCI group mean?=?16.86, SD?=?1.96; AD group mean?=?17.23, SD?=?3.72) [F(2,46)?=?0.478, p?=?0.62]. The mean Mini Mental State Examination scores were 29.31 (SD?=?0.75, range 28–30) for the NC group, 27.83 (SD?=?1.80, range 25–30) for the aMCI group, and 24.44 (SD?=?2.76, range 20–29) for the AD group. Mean scores in the AD group were significantly lower than in the NC and aMCI groups (p??0.001).

All participants were community-dwelling individuals who were right-handed and had normal or corrected-to-normal visual acuity. Participants were recruited from the University of Kentucky Alzheimer’s Disease Center (UK-ADC) longitudinal normal volunteer cohort [22, 23]. Inclusion criteria for this cohort are a minimum age of 65 years, cognitive and neurological normality at enrollment, agreement to brain donation to the UK-ADC at death, a designated informant for structured interviews, and willingness to undergo annual examinations. Participants were excluded from the cohort if they had a history of substance abuse, major psychiatric illness, or neurological disease. The annual evaluation includes a comprehensive neuropsychological battery and general physical and neurological examinations that are detailed elsewhere [24, 25].

If any of the following occurs, a cohort participant is evaluated with a more detailed cognitive assessment and formal clinical assessment by study physicians: (1) diagnosis by the examining physician of conversion to MCI or dementia; (2) suspicion of cognitive decline on the part of the supervising neuropsychologist and/or objective decline in the form of annual memory test score 1.5 SD below the previous annual assessment, which is done annually in the UK-ADC consensus conference review [24]; (3) prescription of a cholinesterase inhibitor, N-methyl-d-aspartate antagonist, or other treatment associated with the medical diagnosis of dementia by an outside physician; or (4) evidence of functional impairment secondary to cognitive decline from the participant or an informant. The UK-ADC consensus conference reviews these data and a diagnosis of normal, aMCI [1, 26–28], or AD [29] is assigned in accordance with the National Alzheimer’s Coordinating Center’s Uniform Data Set procedures [30]. After conversion to aMCI or AD, each cohort member participated in the present study’s EEG protocols as soon as their scheduling permitted (i.e., most often within 1 month of diagnosis).

EEG and behavioral data analyses performed with a subset of this cohort have been published previously [25, 31, 32]. All participants provided written informed consent before participation. This study was approved by the institutional review board (IRB) of the University of Kentucky.