At Starlab, we’re constantly exploring how EEG-based research can help us better understand brain function in different populations. One method we often use to study attention and the brain’s ability to process and evaluate new information is the auditory oddball paradigm, a simple yet powerful task. This method can reveal changes in brain activity that provide insights into cognitive health, including early signs of Alzheimer’s Disease (AD).
How Does the Auditory Oddball Paradigm Work?
Participants hear a series of sounds, most of which are the same, like a “beep” tone. Occasionally, they’ll hear a different, “oddball” tone or "target" tone—a sound that stands out. When participants hear the oddball, they’re asked to mentally note it or press a button. The task is designed to capture attention and memory processes because participants must detect the rare tone among a stream of repetitive ones.
EEG recordings capture brain responses to these tones, helping us observe “event-related potentials” (ERPs)—specific changes in brainwave activity that occur in response to particular stimuli. This process reveals how the brain is processing and responding to different sensory events.
How Do We Capture Clear Brain Signals? Averaging Epochs
When we conduct an auditory oddball experiment, the EEG records brain activity for each sound (whether it’s a standard or oddball tone). However, a single response—called an epoch—is often filled with noise from various sources, like muscle movements or other background brain activity. By repeating the standard and oddball sounds multiple times (typically around 80-100 standard tones and 20-40 oddball tones), we can record many epochs and average them together. This process cancels out random noise and reveals the “true” brain response to each type of sound.
Key ERP Components: N200 and P300
In the auditory oddball task, two ERP components are of particular interest: the N200 and P300.
N200: The N200 is a negative-going wave ("N") and appears around 200 milliseconds after the oddball tone. It reflects early attention and the brain's ability to recognize something as different or unexpected.
P300: The P300 is a positive.-going wave ("P") and occurs around 300 milliseconds after the oddball and is related to memory and cognitive processing. It’s thought to reflect how the brain evaluates and categorizes a stimulus.
Auditory Oddball and Cognitive Decline
In collaboration with ACE Alzheimer Research Center, we conducted a study using the auditory oddball task with participants experiencing different stages of cognitive decline. This included people with Subjective Cognitive Decline (SCD), Mild Cognitive Impairment (MCI) with positive AD biomarkers collected from cerebrospinal fluid (MCI+), and MCI without AD biomarkers (MCI-). Our study revealed an interesting trend: participants with MCI, especially those with positive AD biomarkers, showed a reduced P300 response compared to those with SCD.
Below is a plot illustrating this trend, where the P300 response gradually diminishes as we progress from SCD to MCI and is lowest in the MCI+ group.
Why Does the P300 Response Decrease?
So, why might we see this reduction in the P300 among participants with MCI, and particularly in those with AD biomarkers? The P300 is associated with attention, memory, and the brain’s ability to process and evaluate new information. A decrease in the P300 could indicate that the brain’s efficiency in these cognitive processes is weakening, making it harder for individuals to recognize and respond to new information quickly. This effect is more pronounced in MCI+ participants, suggesting that as Alzheimer's pathology progresses, the brain’s cognitive resources are further compromised.
This insight aligns with other research showing that the brain's ability to allocate resources efficiently often decreases in the early stages of Alzheimer's. By examining ERP components like the P300, we hope to gain a clearer picture of the subtle brain changes that may precede more noticeable cognitive symptoms.
Want to learn more?
Stay tuned for the following posts where we will explore other tools from the Starlab's Battery of Cognitive Tasks!
More details on the use of EEG for Cognitive Decline and Alzheimer's Disease here:
and here:
Comments