A recent study has shown that repetitive transcranial brain stimulation (rTMS) improves memory by making the network of cortical areas active, which interacts with deep memory, the hippocampus.
With the use of rTMS in psychiatry, and it has been approved by the U.S. Food and Drug Administration (FDA) as a treatment for depression. The results of the study have important potential neuroscientific implications – suggesting all the ways to manage it – which is important, but it’s at the deepest part of the hippocampal structure when no surgical procedure is done.
Before the use of rTMS, no one could target the network of brain areas associated with memory.
Joel Voss, PhD, assistant professor of medical sociology at Northwestern University, Feinberg School of Medicine in Chicago, Illinois, and his colleagues conducted research on rTMS and found that TMS can improve memory through cortical networks. The article was recently published in the journal.
The central idea of the rTMS study is that you only have an effect on specific superficial parts of the brain, and in fact we can stimulate directly here. That’s because the current can’t get into the very deep parts.
But let’s look at the parts of the brain close to the surface where we think the damage is causing the memory impairment, is it possible to stimulate these parts and affect changes in most of the hippocampal network, and we found that the knot answer is: correct.
The high frequency of repetitive transcranial brain stimulation showed that the stimulated parts emitted yellow cone-shaped energy on top of the lateral brain of the head. The stimulation increased the interaction of memory-related brain networks, including the part of the brain region marked in purple.
The core structure of this network is the hippocampus, which is deep in the brain and is represented by images.
Healthy adults
This study included 16 healthy adults, aged 21-40 years, who received 20 minutes of rTMS treatment per day for the past 5 days of treatment.
Prior to treatment, patients were assessed with functional magnetic resonance imaging at rest to determine the location of the cortico-hippocampal network cortical area, which is assumed to be the memory-related brain area and the target of the corresponding rTMS signal.
The control conditions for the placebo group were, lowest lower limit of neural stimulation that elicited a response, post-treatment MRI assessment, and doing 24-hour follow-up stimulation, which showed a significant and substantial increase in connectivity compared to the baseline we knew, and these were the baselines for four brain areas of hippocampal connectivity: precuneus/postpressure cortex, syrinx/parahippocampal cortex, superior parietal gyrus, and left parietal lobe.
Similarly, when considering experiments with memory-related facial cues and verbal cues, after 24 hours of treatment, participants showed a corresponding improvement compared to baseline, which was significant when compared to the placebo group (p= .008).
Participants showed a large change in stimulus-sensing connectivity on fMRI, indicating a large improvement in memory.
The authors noted that the fMRI connectivity changes were striking, especially in the hippocampus, and that a one-to-one correspondence could be found with the improvement in associative memory.
And when cortical motor areas are different from the hippocampal cortical network, they are not stimulated in control experiments, which provides a strong evidence against a possible non-specific effect.
The current strength of rTMS is 3 Tesla, which is very strong – roughly equivalent to 100,000 times the Earth’s magnetic field – and drops down immediately after leaving this part, thus penetrating less than 1 cm deep into the brain. Side effects are minimal and very rare, and in the current study the authors did not see side effects.
When it comes to long-term effects, we can’t be sure, but just looking at the magnitude of the effects on the brain, it’s unlikely that there will be any lasting effects after a few days.
The results of this study, with sustained improvement after 24 hours of treatment, are particularly noteworthy, while encouraging possible therapeutic applications for those with memory impairment.
An exciting thing related to this is that we can actually modulate this memory network and we can investigate different disorders such as stroke, mild cognitive impairment, traumatic brain injury, and even schizophrenia, which can improve symptoms to some extent and hopefully affect people’s memory.
Important Perspectives
Neurologist Dr. Daniel C. Potts, a member of the American Academy of Neurology and associate physician-in-chief at the University of Alabama, Tuscaloosa, says he endorses this study, which offers a new perspective on the role of rTMS in memory.
I think the results of this study, although the conclusions obtained are on a very small topic and need to be confirmed by more studies, are exciting and give us hope.
He noted that early studies reported from Toronto, Ontario and Canada noted that for patients with schizophrenia, rTMS
had improved their motivational systems, learning and working memory, including recent learning. However, the latest study appears to be the first of its kind.
For me, the main clinical implication is that rTMS appears to enhance functional connectivity, as well as targeted function on neural memory circuits, including inducing changes in neuroplasticity, which may be more durable.
Although I think it is too early to put it into action and make it public, there is clearly promise for rTMS in enhancing memory function in patients with cognitive impairment, even those with underlying dementia or Alzheimer’s. The application of this technique in Alzheimer’s disease is a meaningful new approach to this disease.
Because of the adverse effects of the pathophysiology of Alzheimer’s disease on hippocampal structure and function, the most important clinical implications are to be based on the idea that the remaining hippocampal tissue can be assumed to be a circuit, contained in the circuit of memory, and therefore can preserve or enhance that function.