P300 (Latency) Event-Related Potential: An Accurate Predictor of Memory Impairment

Abstract

To determine if P300 latency changes precede and correlate with memory and mental status, patients (N=1506 aged 20–100 years) who received medical and psychiatric diagnoses (from 1997 to 2002), were assessed for P300 (N=1496), WMS-III (N=694), and MMSE (N=456). Patient and control groups included, a) normal WMS-III on all 4 subscales (N=36), b) normal WMS-III and MMSE (N=189) with subjective memory/mental status complaints, and c) medical patients with normal WMS-III and no memory complaints (N=205), and d) P300 control group without medical, psychiatric or memory problems for ROC.

Patients with impaired/borderline memory had a prolonged P300 latency (P<0.02) compared to age matched non-impaired controls; in patients with normal WMS-III/MMSE, with subjective mild memory/mental status impairment, P300 latency was prolonged compared to controls (P=0.0004). The P300 latency increased by 0.72ms per year (P=7.9×10⁻⁶⁵) and voltage decreased by 0.03dV per year (P=6.7×10⁻¹⁰), and both parameters were linearly correlated with the age of the subjects.

Male subjects had an average voltage of 6.1dV and female 6.8dV(P=0.00009). Statistically, prolonged latency began at age range 41–50 (P=0.0002); reduced P300 voltage began at age range 51–60 (P=0.003). WMS-III memory decline for all measures began in females at age range 61–70 (P value at least=0.02) and for males at age range 61–80 (P=0.02). Prolonged P300 latency (P≤0.0001) and memory impairment (at least <0.02) were greater for females than males. MMSE memory decline, male and female, began at age range 81–90 (P value of at least 0.00007).

In our logistic regression model P300 latency was more predictive of WMS-III impairment than MMSE >24. In patients whose WMS-III score is impaired ≤69, or borderline ≤79 (P at least =0.004), a P300 latency more prolonged than the norm (≥300 + 30 + Age) identifies these patients, whereas a MMSE >24 failed. With the ROC curve, we confirmed that P300 latency could accurately identify borderline/impaired memory.