The methodology for collecting high-density event-related potential data while patients with Alzheimer’s disease perform a recognition memory task is reviewed. This protocol will include subject preparation, quality assurance, data acquisition, and data analysis.
Our laboratory uses event-related EEG potentials (ERPs) to understand and support behavioral investigations of episodic memory in patients with amnestic mild cognitive impairment (aMCI) and Alzheimer’s disease (AD). Whereas behavioral data inform us about the patients’ performance, ERPs allow us to record discrete changes in brain activity. Further, ERPs can give us insight into the onset, duration, and interaction of independent cognitive processes associated with memory retrieval. In patient populations, these types of studies are used to examine which aspects of memory are impaired and which remain relatively intact compared to a control population. The methodology for collecting ERP data from a vulnerable patient population while these participants perform a recognition memory task is reviewed. This protocol includes participant preparation, quality assurance, data acquisition, and data analysis. In addition to basic setup and acquisition, we will also demonstrate localization techniques to obtain greater spatial resolution and source localization using high-density (128 channel) electrode arrays.
1. Set up the EEG Equipment
2. Set up the Stimuli Presentation and Data Acquisition Computers
3. Participant Preparation
4. Digitizing for Source Localization and Electrode Placement
5. Data Acquisition for both EEG Data and Experiment
6. Data Post-Processing Pipeline
7. Representative Results
Our work has shown that the early frontal old/new effect (hits > correct rejections), typically associated with conceptual processing or memorial familiarity, remain intact for pictures in patients with mild Alzheimer’s disease compared to healthy older adults, but not for words (Ally, McKeever, Waring, & Budson, 2009). Ally et al. (2009) have shown that the parietal old/new effect, typically associated with recollection, is impaired in patients for both pictures and words compared to their peers. In other words, the frontal memorial processes associated with recognition appear to be similar for pictures between the patients with AD and healthy older adults. In contrast, these processes are impaired for words in patients when we examine differences between the two groups. This significant difference between the groups is evident for posterior memory processes for both pictures and words. Although there has been considerable debate as to the cognitive process associated with the early frontal effect, we hypothesize that patients with mild Alzheimer’s disease can successfully utilize conceptual processing or memorial familiarity to increase their discrimination for pictures compared to words, and these processes likely underlie the robust picture superiority effect in patients with Alzheimer’s disease.
Frontal ERP activity associated with the successful retrieval of words and pictures is demonstrated for patients with very mild Alzheimer’s disease and healthy older controls (Figure 1). These images were taken during the 300 to 500 ms time interval typically associated with conceptual processing or memorial familiarity. Notice the similar frontal old/new effect for pictures (red pseudocolor) but diminished effect for words between groups. (cyan pseudocolor).
Figure 1:Representative ERP Activity During Retrieval Task in Alzheimer’s Patients and Healthy Subjects.
ERPs and behavioral data can provide us with different and complementary information. Whereas behavioral data informs us about the patients’ performance, ERPs allow us to record discrete changes in brain activity. Due to their excellent temporal resolution, ERPs have proven very useful in dissociating and understanding the role of memorial processes (e.g., conceptual processing and familiarity, recollection, post-retrieval monitoring processes) that have been previously associated with specific old/new components of the ERP wave (early frontal, parietal, late frontal, respectively) (see Ally & Budson, 2007). In studying patients with cognitive impairment, event-related potentials (ERPs) are extremely useful in understanding brain physiology, particularly when obtaining meaningful behavioral data is difficult (Ally, 2011). However, there are many pitfalls faced when interpreting ERP data in these populations. For example, due to the heterogeneity of Alzheimer pathology, ERP data from patients often have significant variance between subjects. The current protocol highlights ways in which the variance can be minimized. The results from this protocol help to understand the cognitive and neural underpinnings of memory loss associated with mild Alzheimer’s disease, and to help elucidate which memorial processes are impaired and which are relatively intact in mild Alzheimer’s disease. Our work reveals that some frontally-mediated memory processes, perhaps conceptual processing or memorial familiarity, remain intact for pictures in patients (Ally et al., 2009). This understanding may in turn allow new drug therapies and early behavioral interventions to be developed and keep patients engaged and living in the community for longer periods of time.
The authors have nothing to disclose.
This protocol was supported by the National Institute on Aging grant K23 AG031925 and R01 AG038471.
Product | Company |
BioSemi Active Two EEG Acquisition System* | Cortech Solutions, Inc. |
Polhemus Patriot Digitizer | Cortech Solutions, Inc. |
E-Prime 2.0 Professional Software | Psychology Software Tools, Inc. |
* This system includes the amplifier, Active Two EEG caps, syringes, SignaGel (conductive gel), and facial electrode stickers.