Attentional function in patients with mild Alzheimer disease and those with mild cognitive impairment

Aihong ZHOU; Yinhua WANG; Xiaolin ZHOU

ABSTRACT

BACKGROUND:

Memory impairment is the main manifestation of Alzheimer disease (AD) and mild cognitive impairment (MCI) conspicuous in the early stage. However, such patients very often develop attentional dysfunction, which may affect their normal work and daily life.

OBJECTIVE:

To investigate the attentional function, including continuous attention, selective attention and divided attention, of patients with mild AD and of those with MCI.

DESIGN:

A case-control study.

SETTING:

Department of neurology of a university hospital and department of psychology in a university.

PARTICIPANTS:

The research was completed in the Laboratory of Neuropsychology, the First Hospital of Peking University from November 2003 to January 2004. Totally 18 patients with mild AD and 19 with MCI were enrolled in this study, with 20 normal elderly subjects also included to serve as the normal control group.

INTERVENTIONS:

Several tests were designed to assess the attentional functions of all the subjects, including continuous performance task (CPT) test for assessing continuous attention, simplified Stroop test for selective attention, and dual task test for divided attention.MAIN OUTCOME

MEASURES:

The reaction time (RT) and the percentage of false response were recorded in CPT test and Stroop test, and performance decrement in dual task test was observed.

RESULTS:

In CPT test, the RT of mild AD patients was much longer, and the rates of missing and false responses were higher than those of normal control group [(539.29±103.86) vs (458.47±40.87) ms, 4.08% (3. 13, 13.64) vs0.91% (0.60, 1.90), and 1.51% (0.64, 2.54) vs 0.43% (0.37, 0. 84), respectively, P ＜ 0. 05]. The difference between MCI group and normal control group failed to reach statistical significance. The rate of missing response of all the three groups grow higher with the prolongation of time, with the highest occurring in the third 5 minutes of the test.More AD patients showed sustained attention deficiency after 10 minutes of test (33.33% within 10 minutes and 77.8% within 20 minutes). In Stroop test, all the three groups tended to make more false responses under incongruous condition[11.25% (7.50, 22.50), 2.50% ( -2.50, 5.00), 2.50% (0.00, 4. 38) ], exhibiting significant interference effect, which was the most obvious in mild AD group ( P ＜ 0.05). Patients with mild AD responded more slowly than MCI patients and normal control subjects [ (579. 19 ± 89.93) ms,(524.28 ± 68. 96) ms, (486. 75 ± 51.58) ms, respectively, P ＜ 0.05 ]. MCI group made more false responses than normal control group during the whole course of the test as well as under coincident and neutral conditions[5.83% (4. 17, 8.33) vs2.92% (1.67,3.96); 5.00% (2.50, 7.50) vs0.00% (0.00, 2.50); 5.00% (2.50, 10. 00) vs 2.50% (0.00, 5.00), P ＜ 0. 05]. In dual-task test, a significant decrement in mild AD patients was noted without statistical difference between MCI and normal control group[ 1.03 (0.49,3.75),0.46 (0.08, 1.02),0. 10 ( -0.25, 0. 64), P ＜0.05]. Within mild AD group, more patients showed deficiency in Stroop test and CPT test than in dual-task test (81.25%, 77.8%, and 29.41%, respectively).

CONCLUSION:

Patients with mild AD suffer impairment in continuous,selective and divided attentions, especially obvious in the former two attentional functions. MCI also impairs selective attention as compared with normal aged subjects, with the continuous and divided attention remaining normal. Mild AD patients, MCI patients and normal elderly subjects all show decreased continuous attention, and longer time (than 10 ninutes) of CPT may more sensitively identify continuous attention deficit.