Written By: Juliana Morsello
Introduction
Alyssa has been diagnosed with Major Depressive Disorder. One afternoon, her friend Sarah returned home from a vacation and decided to speak to Alyssa about her time away. Alyssa, who felt completely overcome with sadness and mental fatigue, struggled to fully engage in their conversation. She found herself forgetting parts of Sarah’s story and could not listen nor respond appropriately. Besides her troubles with social interaction, Alyssa also experienced difficulty with remembering tasks and following through with simple instructions given by her parents.
Alyssa made the decision to see a neuropsychologist with some encouragement from her friends and family, who were worried about these problems. The neuropsychologist found that Alyssa had severe working memory deficits after administering a number of cognitive tests (e.g., the Digit Span). These deficits, according to her neuropsychologist, were attributed to her depression.
In this article, we will discuss the impact of working memory deficits on individuals like Alyssa who have Major Depressive Disorder.
Working Memory
You use your working memory when you are doing mental math, trying to retain a phone number, or recalling key details in a storyline while reading. Working memory, also referred to as short-term memory, is the cognitive system that allows us to temporarily store and work with information as we perform complex tasks (Cowan, 2008).
In 1974, Baddeley and Hitch proposed their initial Working Memory Model, which divides short-term memory into three components: the “phonological loop,” the “visuospatial sketchpad,” and the “central executive” (Adams et al. 2018). The phonological loop holds verbal information, while the visuospatial sketchpad holds visual details about object appearance and location. The central executive directs the flow of information to these components and helps control our attention (think of it like a ‘boss’ that oversees the working memory system).
For instance, when you repeat a phone number to yourself in order to remember it later, you are using the phonological loop, which temporarily stores the numeric sequence. If you mentally rehearse a phone number while conversing, you are using the central executive. The central executive can help you shift your attention between keeping the digits in your working memory and processing the conversation.
Long-term memory, which will not be discussed in this article, is a type of memory that is stored for an extended period of time (APA Dictionary, 2018). In 2000, Baddeley and Hitch added a component to the Working Memory Model called the episodic buffer (Adams et al., 2018). This component combines information from working memory and long-term memory to create “episodes” (Baddeley, 2000). For instance, you use your episodic buffer when trying to recall a recent vacation. It combines memories of the sights (visuospatial) with more permanent memories, such as the activities you enjoyed. This helps form a comprehensive memory, or episode, of the vacation experience.
In this article, we will review research on each working memory component in individuals who have Major Depressive Disorder.
Major Depressive Disorder
Major Depressive Disorder (MDD) is a common mental health condition that is characterized by extreme sadness and other symptoms that interfere with daily life (Bains & Abdijadid, 2023). According to the World Health Organization (WHO), MDD is the third leading contributor to poor health worldwide. In fact, it has been predicted that MDD could top the list by 2030. This disorder is believed to be caused by various factors such as genetic predispositions toward MDD, abnormal brain chemistry, and interpersonal stressors.
To receive a diagnosis of MDD, according to the Diagnostic and Statistical Manual of Mental Disorders (5th ed.; DSM-5; American Psychiatric Association, 2013), individuals must experience five or more symptoms for at least two weeks. One symptom must be persistent low mood or a loss of interest in previously enjoyed activities (anhedonia). The other symptoms can include disturbances in sleep, decreased energy levels, difficulty making decisions, and feelings of worthlessness or guilt, for example.
“Brain Fog”
Multiple studies have found that people with MDD struggle with memory and concentration (Parker, 2022). Neuroscientists and psychologists refer to these symptoms as cognitive deficits, but you may know them as “brain fog.” Dr. Parker, an academic psychiatrist (n.d.), observed that while patients may not explicitly state that they suffer from brain fog, they make statements consistent with the concept, like “My thinking is cloudy” and “I also do all the cooking at home, but when I'm depressed, I can't remember the recipe for an omelette” (Parker, 2022).
Working Memory and MDD
A type of memory that individuals with MDD commonly experience difficulties with is working memory (Nikolin et al., 2021). For instance, the cooking scenario stated above is a good example. You use your working memory to retain the order when you have to follow a recipe step-by-step. Therefore, it may be a sign of impaired working memory if a depressed person claims they are unable to finish a task like this.
Next, we will review research on working memory in people with MDD. The following paragraphs will describe the methodology and findings of a study conducted by Shan et al. (2018). We will also discuss research on how impaired working memory affects emotional regulation.
Study Objective and Methodology
In a study by Shan et al. (2018), the researchers aimed to address conflicting literature on how each component of working memory is impacted in people with MDD. To gain a thorough understanding, they had patients with MDD and healthy controls complete a series of tests. The following were the forward Digit Span test, Visual Reproduction subtest, 2-Back task, Symbol Digits Modalities Test, and the Stroop Color and Word Test. Before we review the results of this study, the purpose of each task will be discussed.
Verbal and Visuospatial Tasks
During a forward Digit Span test, participants hear a series of numbers and are asked to verbally repeat them. Because this test requires the temporary storage and manipulation of verbal information, it tests the function of (as I am sure you correctly anticipated) the phonological loop (Goetz, 2007). However, during a Visual Reproduction subtest, participants are asked to draw complex pictures after being briefly exposed to them. This tests the function of their visuospatial sketchpad. Because these tests assess verbal and visuospatial working memory, respectively, which are included in the episodic buffer system (Shan et al., 2018), a low score on either of them can indicate impairments in the episodic buffer.
“Updating” Task
The 2-Back task, Symbol Digits Modalities Test, and Stroop Color and Word Test measure central executive functioning (Shan et al., 2018). As mentioned earlier, the central executive manages our attention, and it does so in three ways: updating, shifting, and inhibiting (Rodríguez-Nieto et al., 2022). Updating is the process that helps us keep track of changed information, which is required during the 2-Back task. During this task, participants must indicate whether the stimulus they are currently seeing (e.g., letters) matches the one presented two trials earlier (Felver-Gant et al., 2007).
“Shifting” and “Inhibition” Tasks
Shifting involves mentally switching between different tasks (refer back to the phone number example from earlier) (Rodríguez-Nieto et al., 2022). This process is necessary when taking the Symbol Digits Modalities Test. Participants are instructed to alternate between focusing on geometric figures and a reference key containing numbers that they must pair the figures with (WPS, n.d.).
Inhibiting refers to the process of suppressing irrelevant information while performing a task. For example, during the Stroop Color and Word Test, one has to specify the color of ink in which a word is printed, rather than the word itself (Scarpina & Tagini, 2017). If “RED” is printed in blue ink, you should say “blue.” This requires you to suppress your automatic response to read the word and instead concentrate on the color of the ink.
Findings
Shan et al. (2018) found that patients with MDD performed significantly worse on each test than the healthy controls, which suggests that they were impaired in all known components of working memory. Additionally, the researchers found that patients with MDD had lower levels of specific chemicals in the prefrontal cortex than healthy controls, which could explain their test performance. This is because the prefrontal cortex is a brain region involved in working memory. Consequently, it may be difficult to temporarily store and use information while completing tasks if one's prefrontal cortex is not working properly.
Updating, MDD, and Emotional Regulation
Individuals with MDD who struggle to update information may have difficulty regulating their emotions effectively. It has been argued that depressed people struggle to update negative thoughts with new, more positive information (LeMoult J., & Gotlib I. H., 2019), which may lead to long-term self-criticism. For instance, consider a scenario where a person with MDD is given constructive, negative feedback at work. Even after making improvements based on feedback and receiving praise, they may still perceive their performance as inadequate due to their difficulty in updating negative self-perceptions. This ongoing self-criticism can contribute to prolonged feelings of low self-worth and make recovery more difficult.
Repetitive negative thinking, such as that above, is called rumination (Songco et al., 2023). According to Chen (2023), research indicates that adolescents who ruminate more frequently have higher levels of depression symptoms and lower working memory functioning. In response, researchers have investigated methods for enhancing working memory among those with MDD. Working memory capacity has been found to be sustainedly increased with long-term working memory training, as opposed to short-term training. However, despite its benefits, long-term training is not universal. Chen (2023) notes that this is due to the significant level of engagement required and the considerable time needed for it to effectively improve working memory, which is time that adolescents may not have.
Why This Matters…
Working memory deficits can significantly impact day-to-day life. For instance, consider the findings of Shan et al. (2018) in a larger context. A person with an impaired phonological loop may find it difficult to retain verbal information, such as complicated instructions and deadlines, or engage in in-depth conversations. These challenges may contribute to the frustration and feelings of inadequacy that many people with MDD experience. Furthermore, the study suggests that tasks requiring updating, shifting, and inhibiting are difficult for individuals with MDD. This can have an impact on their ability to manage time and prioritize their tasks effectively. Notably, these difficulties are especially relevant for college students and those in the workforce, who may have to juggle multiple responsibilities while also dealing with MDD.
To enhance the quality of life for these individuals, more research is needed on treatment options. While psychotherapy (also known as talk therapy) is commonly used, there is evidence that cognitive training and physical therapy can also improve cognitive processes like working memory, although fewer studies have focused on these interventions in people with depression (Chen, 2023). Therefore, more research in this area is necessary to provide effective long-term relief from the everyday difficulties posed by working memory deficits.
According to Soczynska et al. (2014), medications such as Bupropion and Escitalopram have shown promise in improving verbal and non-verbal working memory in individuals with MDD. It is important to keep in mind, however, that due to possible risks, antidepressants are typically not advised for people younger than 18. Researchers should continue studying low-cost, at-home alternatives to therapy for younger adolescents who might not be able to take certain medications and anyone who cannot afford psychotherapy, cognitive training, or physical therapy. For example, there is growing research on the impact of meditation on working memory (e.g., Youngs et al., 2021).
Given that time constraints may prevent individuals from receiving long-term treatment, researchers should study the efficacy of more intensive but shorter treatments to determine whether they have long-term effects. Overall, further study in this area is critical for improving outcomes for people coping with MDD in academic, professional, and personal settings.
Footnote:
I hope that you learned more about working memory and MDD! For anyone that needs further clarification or wants to learn more, I have provided some resources below:
Working memory: https://www.simplypsychology.org/working-memory.html
MDD: https://my.clevelandclinic.org/health/diseases/24481-clinical-depression-major-depressive-disorder
Although we did not discuss cognitive remediation as a method to treat working memory deficits, I wanted to provide some resources on this in case you and/or someone you know could benefit from it :) - https://www.webmd.com/depression/cognitive-remediation-major-depression; https://positivepsychology.com/cognitive-remediation-therapy/ https://www.sciencedirect.com/science/article/abs/pii/S0165032721001208?via%3Dihub
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