Academic Biography

At the time this grant was awarded, Dr. Heather McNeely was Head of the ERP Laboratory and assistant professor in the Department of Psychiatry at the University of Toronto.  She is currently assistant professor in the Department of Psychiatry and Behavioural Sciences at McMaster University, Director of Training in the Psychology Residency Program, and Clinical Neuropsychologist in the Schizophrenia Service at St. Joseph’s Healthcare Hamilton.  Her research focuses on the impact of emotion on the biology underlying cognitive processes in healthy populations and in populations diagnosed with major depressive disorder and schizophrenia.

What is Major Depressive Disorder?

Major depressive disorder (MDD) is a mental illness characterized by persistent feelings of sadness, perceived helplessness, irrational guilt, negative thoughts, impaired attention and memory, and difficulty focusing on relevant information.  MDD is one of the most prevalent mental illnesses: approximately 4% of Canadians are diagnosed with depression each year.

Project Summary

Dr. McNeely and her team conducted an electrical brain mapping study to investigate and characterize how depression affects a person’s ability to control his or her thoughts on the biological level.  Dr. McNeely’s team focused on cognitive inhibition (a thinking skill that allows a person to ignore or inhibit thoughts at will) deficits.  They recorded the electrical brain activity in 15 participants diagnosed with depression (or depression in partial remission) and 14 healthy participants, throughout a modified reaction-time test and then compared the behavioural and electrical brain activity results between the two groups.

Biological Background and Rationale

Depression has both psychological and biological causes, but the links between the biological abnormalities in the brain and thought disorders specific to depression are not well understood.  Cognitive inhibition deficits, specifically the inability to ignore negative thoughts, may put people at a greater risk of developing depression or relapsing after a period of remission. 

To locate the regions where cognitive inhibition deficits occur, Dr. McNeely and her team recorded the real-time electrical brain activity of all the participants while they completed an emotional Stroop task.  This is a reaction time test where participants are shown a neutral or emotionally meaningful word, positive or negative, in a colour font – and are asked to identify the font colour.  Each participant’s electrical brain activity was recorded as event related potentials (ERPs: characteristic electrophysiological responses to stimuli, directly related to a thought or perception).  During neuron-to-neuron communication, when a neuron receives a chemical message from another neuron it conducts an electrical current (an electrophysiological response) and can send a chemical message to another neuron.  In this experiment, the participants wore caps embedded with electroencephalography (EEG) electrodes that detected and analyzed these small electrical currents.  This method allowed Dr. McNeely and her team to locate the neural structures involved in completion of the emotional Stroop task that directly corresponded to the steps of the task.

During the emotional Stroop task, the participants were asked to ignore the meaning of the word and identify the font colour as quickly as possible.  This task is used to find the interference in response time: the response time for the neutral words can be affected by the conflict between the instinct to read the word rather than name the colour, but additional factors may increase the response time for emotionally meaningfully words.  In an earlier experiment Dr. McNeely compared the behavioural performance and electrical brain activity in a similar emotional Stroop task between participants diagnosed with schizophrenia and healthy participants.  She found that electrical brain activity varied between the two groups, but there was no difference in observable behaviour between the groups.

Outcome

Dr. McNeely and her team found that participants diagnosed with depression (or depression in partial remission) were able to perform the emotional Stroop task as well as the healthy participants: the reaction times and accuracy scores did not vary significantly between groups.  However, the ERP recordings indicated significant differences in electrical brain activity between the groups.  The depressed group showed altered ERP activity relative to the control group, indicating that they had difficulty controlling cognitive processes when they were shown emotionally meaningful (both positive and negative words) words. 

In summary, the researchers found alterations in the functioning within specific regions of the brain that form a biological link to problems in cognitive inhibition and the negative thought patterns that arise from this inability.  By locating the physical sources associated with cognitive inhibition deficits specific to depression, Dr. McNeely and her team made significant progress in research for better treatment for depression.