TMS Advances

Study Suggests TMS Therapy Can Reactivate Latent Working Memories


Cognitive psychology is the branch of psychology that studies the mind as an information processor, which includes the study of memory.

Recently, a study has shown a correlation between transcranial magnetic stimulation (TMS) and its activation of items held in working memory (WM). Simply put, WM is the section of your short-term memory (STM) where you store things while you are thinking. In addition to being a storage medium, it is also a place where information may be manipulated. 

TMS, generally known as the emerging FDA-approved solution to treatment-resistant depression, is now making its way onto the cognitive psychology scene by showing that it has possible implications on this model of WM.

Before the WM theory came about in cognitive psych, Atkinson and Shiffrin’s (1968) “multi-store model” was the most popular theory on memory.

While the Atkinson-Shiffrin model served psychology well but generating plenty of research on memory, researchers such as Baddeley and Hitch (1974) felt dissatisfied with the model’s inability to cover everything concerning STM and criticized it as too simplistic. 

In brief, this was due to the fact that, according to the Atkinson-Shiffrin model, the STM—a single system—holds limited information. However, Baddeley and Hitch recognized that the STM is comprised of a few different subsystems in a new theory that they proposed as WM. Thus, WM effectively replaced STM in cognitive psych. 

According to Baddeley and Hitch, WM is comprised of one “supervisory system,” the central executive and two subsystems, the visuospatial sketchpad and phonological loop. 

But now, the TMS-WM research is challenging Baddeley and Hitch’s long-standing theory on WM.

Read on in this article to find out more on:

  • Working memory: What it is, how it works, and why it matters
  • The synaptic theory and TMS: Defining the two before we see how they relate

Working Memory 

When Baddeley and Hitch proposed their theory on WM in 1974, it was to replace the then-underdeveloped theory of STM that was championed by Atkinson and Shiffrin in 1968. 

Pictured is a brief visual representation of Baddeley and Hitch’s working memory model, which replaced the understanding of short-term memory that was, until then, only understood as a singular system. Baddeley and Hitch challenged that notion by suggesting that STM has multiple subsystems. 

In this section, we’ll break down the sections of the WM: 1) the central executive and the subsections, 2) the phonological loop, and 3) the visuospatial sketchpad. Then, we’ll briefly take a critical look at how the WM model serves cognitive psychology and what it might be missing.

Central Executive

According to Baddeley and Hitch, the central executive is the most important component of the WM model. 

It is responsible for monitoring and coordinating the two subsystems, i.e. the visuospatial sketchpad and phonological loop, and relaying information to the long-term memory (LTM).

Essentially, the central executive has to decide what information is attended to. This is crucial, because we are constantly inundated with visual and auditory information, so we need to filter out a lot of that information in order to survive. 

A practical example of the central executive’s decision-making is when the tasks of driving a car and talking conflict. Say you’re driving down the street having a conversation with your friend who is sitting in the passenger seat when a pedestrian starts wandering onto the road where they shouldn’t be. Instead of continuing to have a conversation with your friend, you will likely stop talking to focus on the road so that you don’t hit the pedestrian. That decision is the central executive of your WM at work.

You might not realize it, but we are inundated with information all the time—but the average brain is able to select what information is most necessary to pay attention to and what is not. So when you’re driving and your friend is talking to you from the passenger seat, but you need to focus, you might tune out of the conversation for a little while. 

Thus, the central executive is a system that controls attentional processes more than it is a memory store. On the other hand, the phonological loop and visuospatial sketchpad are specialized storage systems. The central executive merely helps us selectively attend to some stimuli and ignore others.

Phonological Loop

The phonological loop is one subsystem of the WM, and it is the part that deals with spoken and written material. It consists of two parts, the phonological store and the articulatory control process.

The phonological store, or the “inner ear,” holds information in the form of speech for 1-2 seconds at a time. Speech enters the store directly, but written words must be converted into an articulatory (spoken) code before they can enter the store.

The articulatory control process, or the “inner voice,” rehearses information from the phonological store and is linked to speech production. In other words, it circulates information like a tape loop over and over, which is how we remember a telephone number we have just heard. So long as we keep repeating the number, we can retain it in WM. The articulatory control process also converts writing into an “articulatory code,” or “inner speech,” and transfers it to the phonological code.

Visuospatial Sketchpad

The visuospatial sketchpad, also known as the “inner eye,” is the second subsystem of WM. This subsystem deals with visual information, or what things look like.

It is likely that the visuospatial sketchpad plays a role in keeping track of where we are and how we are positioned in relation to other objects. It is important for us to know this information so that we, for example, don’t bump into all the desks and chairs when we are trying to walk through a classroom.

Picture your house. How many windows are on the front of your house? As you’re recalling this number, your visuospatial sketchpad is recalling the layout of your home from your LTM. The visuospatial sketchpad is thought to govern visual information and spatial awareness.

This subsystem also displays and manipulates visual and spatial information held in the LTM. For example, picture the front of your house, and count how many windows there are. The layout of your house is stored in your LTM and is currently being retrieved by your visuospatial sketchpad.

Pitfalls of Working Memory

WM has been empirically proven in multiple studies, primarily by showing that individuals can use different parts of WM at the same time, like in a dual task of digits and verbal reasoning.

However, many critics have come against the WM model for its pitfalls.

One of these pitfalls is that not much is known about how the central executive—claimed by Baddeley and Hitch as the most important part of WM—works at all. This is due to the fact that the central executive, a decision-maker and not a store, is quite difficult to isolate while conducting research. 

Another is that it might not be the case that we need to be “focused” on something in order for it to be in our WM.

An Emerging Theory: Synaptic Theory of WM

The traditional WM model suggests that, for something to occupy the WM, it depends on sustained, elevated activity in the brain. In other words, the “neural basis for WM is elevated and persistent neuronal firing.”

However, researchers are studying how this claim might not necessarily be the case.

Now, a new theory is emerging on WM, called the synaptic theory. This theory claims that information can be held in the WM via synaptic mechanisms that do not require such sustained, elevated brain activity. 

TMS and the Synaptic Theory

Through transcranial magnetic stimulation (TMS) pulses, a kind of “reactivation” of working memories can occur. 

TMS therapy is a non-invasive, drug-free procedure that places a magnetic coil on the scalp to send pulses to the brain. In the US, it is FDA-approved to treat depression and related depressive conditions such as post-traumatic depression. Image courtesy of Medical Associates of Northwestern Arkansas.

When someone shifts their attention from A to B in the WM, the neural representation of A drops to baseline, as though A has been “forgotten.”

However, when TMS pulses briefly reactivate the representation of the unattended item that was thought to be “forgotten,” back into focal attention.

The results found in the study by Rose et. al. (2016) demonstrated exactly this—a “reactivation effect” in the WM. This reactivation effect “occurred and influenced memory performance only when the item was potentially relevant later in the trial, which suggests that the representation is dynamic and modifiable via cognitive control.” Thus, the results support a synaptic theory of WM.

Implications for the Future

This area of TMS research has major implications for cognitive psychology and the WM theory as a whole. It is beginning to phase out the long-standing model proposed by Baddeley and Hitch. 

And importantly, these findings also prove to be methods of strengthening cognitive building blocks and creating the conditions for better high-level cognitive functioning. 

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