TMS for Cognitive Enhancement: Brain Stimulation for Memory, Attention, and Executive Function

Cognitive enhancement is the process of improving cognitive abilities, such as memory, attention, and reasoning, beyond the normal range. Cognitive enhancement can be pursued for various reasons, such as treating cognitive impairments, improving performance, or increasing well-being. Cognitive enhancement can be achieved by various methods, such as therapy, drugs, or technological techniques. Transcranial magnetic stimulation (TMS) is one of the most promising technologies for cognitive enhancement. TMS, a noninvasive technique that uses magnetic pulses to stimulate specific brain regions, can affect brain activity and connectivity, and thus influence various cognitive functions such as memory, attention, and executive function. This article will explore research about how TMS has the potential to enhance such cognitive processes.

Cognitive enhancement

 

The rationale for utilizing TMS for cognitive enhancement lies in the premise that TMS can address abnormalities in brain connectivity and activation, factors often associated with cognitive deficits. However, as neuroscience research explored cognition beyond conventional standards, new definitions of cognitive enhancement have emerged. In addition to treatment-driven cognitive enhancement, TMS is also used for supplementary approaches. TMS stands apart from other non-invasive brain stimulating technologies due to its neurostimulatory nature.1 Studies have shown that healthy individuals undergoing TMS treatments exhibited improvements in episodic memory,2 working memory,3 and motor learning performance.4 Exciting new studies have also introduced the combined use of TMS and neuroimaging techniques such as functional magnetic resonance imaging (fMRI) to identify potential biomarkers for cognitive function.

Mechanisms

 

Repetitive transcranial magnetic stimulation (rTMS) uses magnetic pulses to stimulate specific brain regions. Studies have indicated that rTMS that is delivered prior to a task or in short periods in between tasks can enhance the overall cognitive task performance, and therefore became popularized in the field of cognitive enhancement.1 Of the many studies that focus on the cognitive enhancing effects of TMS, the majority have used rTMS as the primary method of treatment. One of the most widely used techniques for cognitive enhancement is high frequency rTMS (HF-rTMS). HF-rTMS is thought to increase activity of the targeted brain region, leading to improved cognitive performance. Studies have further proven that HF-rTMS has more long-term effects on the cognitive than other types of TMS.1

TMS involves applying magnetic pulses to specific brain regions, but the effects on behavior and thought processes vary based on what brain region is stimulated. One of the most widely studied brain regions for cognitive enhancement via TMS is the prefrontal cortex (PFC), which is located in the frontal lobe. Previous studies have shown that the PFC is activated during cognitive tasks, and that its activation increases with the difficulty of the task. Many studies have also shown that stimulating the particular regions of the PFC with rTMS can improve cognitive performance in different domains, such as inhibition, working memory, verbal fluency, and logical memory.1 Some studies have also found that simultaneously stimulating the PFC on both hemispheres can enhance episodic memory by altering the brain’s oscillatory activity. Oscillatory activity is associated with different states of consciousness, such as wakefulness, sleep, and dreaming and can also reflect different cognitive processes, such as memory, attention, language, and executive functions. Although there have been a few specific studies indicating cognitive improvements from TMS when targeting brain regions outside the PFC, like the left primary motor cortex to enhance associative memory, the majority of research suggests that stimulating the PFC through rTMS produces the most pronounced cognitive improvements.

An Overview: Memory, Attention, Executive Function

 

Memory

The process of memory involves how we acquire, store, and retrieve information. Memory is essential for learning, remembering, and daily functioning. Memory involves three major processes: encoding, storage, and retrieval. Encoding is the first stage of memory, where perceived information is transformed in order to be stored. Storage is the second stage of memory, in which the information is maintained for a period of time. Retrieval is the third stage of memory and involves using the stored information for various purposes. There are several processes necessary for effective memory. Working memory is a component of memory that involves the temporary storage and manipulation of information. Another important component of memory is episodic memory, which involves the ability to recall specific events or experiences. Different brain regions map on to voluntary and involuntary recall in the process of memory retrieval. Relational memory is another component of memory that involves the ability to establish and retrieve information about relationships between different items or events, such as faces and names, words and meanings, or places and landmarks.

Attention

Attention is a fundamental aspect of neurocognitive function that plays a critical role in various cognitive processes. Selective attention is a crucial component of attention that involves the ability to focus on relevant stimuli while disregarding irrelevant ones. Sustained attention is another important component of attention, referring to the ability to maintain focus and concentration over an extended period. Executive attention is a critical component of attention that involves the ability to allocate cognitive resources, switch between tasks, and inhibit irrelevant information. Attentional control is another component of attention that involves the ability to regulate and direct attention based on task demands. In attention-deficit/hyperactivity disorder (ADHD), a neurodevelopmental disorder characterized by difficulties in attentional control, individuals are challenged by impairments in sustained attention, selective attention, and inhibitory control.

Executive function

Executive function refers to a set of cognitive processes that are involved in goal-directed behavior, decision-making, problem-solving, and self-regulation. It plays a crucial role in neurocognitive function and is associated with various brain regions, particularly the frontal lobes. Executive functions are not singular but rather consist of distinct processes related to the pre-frontal cortex that come together for control functions. These processes include inhibitory control, the ability to guide thoughts and behaviors according to goals and plans rather than impulse, cognitive flexibility, the ability to adapt thinking and behavior to new situations or changing demands, and problem-solving.

Enhancing Memory, Attention, and Executive Function with TMS

 

Memory

Enhancing memory with TMS has been the subject of several studies. Studies have found that TMS can enhance episodic memory,5 enhance one’s ability to store and manipulate sensory information acquired through the sense of touch (tactile working memory),6 and improve precision of memory.1 These findings suggest that TMS can affect brain activity and improve memory performance in different contexts. However, further research is needed to optimize TMS parameters and target specific populations.1 Overall, TMS shows promise as a non-invasive technique for enhancing memory function.

Attention

Enhancing attention with TMS has been the focus of several studies. One study demonstrated that they could use TMS to activate the parietal cortex region of the brain, which is activated by attention and linked to perception.7 Another study investigated the effect of TMS on excitability in the visual cortex and found that attention can directly enhance neural networks involved in processing the area of focus in visual space.8 This suggests that TMS can improve visual awareness and attention. Researchers have also found that TMS can be used to improve the ability to control attention,9 enhance the ability to either focus on something important (top-down attention) or make notice something unexpectedly (bottom-up attention),10 and affect the ability to pay attention to things in our environment that demand sudden attention.11 Overall, these studies provide evidence for the potential of TMS in enhancing attentional processes.

Executive Function

Executive functions encompass a range of cognitive processes critical for planning, decision-making, and goal-directed behavior. TMS can optimize executive functions by influencing the pre-frontal cortex, which is largely responsible for these processes. A meta-analysis of over 60 studies including more than 1500 participants found that TMS had significant positive effects of TMS on inhibition in healthy individuals. Inhibition is the ability to suppress or restrain unwanted thoughts, impulses, or behaviors. However, findings were inconclusive about other executive function domains, possibly due variability within study designs. The evidence suggests that TMS has the potential to enhance executive function and improve cognitive performance.

TMS shows potential for cognitive enhancement to improve memory, attention, and executive function. Ethical considerations and personalized approaches will be instrumental in shaping the responsible and effective use of TMS for cognitive enhancement. As our understanding of these approaches advances, the future of cognitive enhancement may see remarkable progress in improving individual cognitive capabilities.

References:

  1. Kim, T. D., Hong, G., Kim, J., & Yoon, S. (2019). Cognitive Enhancement in Neurological and Psychiatric Disorders Using Transcranial Magnetic Stimulation (TMS): A Review of Modalities, Potential Mechanisms and Future Implications. Experimental neurobiology, 28(1), 1–16. https://doi.org/10.5607/en.2019.28.1.1
  2. Gagnon, G., Schneider, C., Grondin, S., & Blanchet, S. (2011). Enhancement of episodic memory in young and healthy adults: a paired-pulse TMS study on encoding and retrieval performance. Neuroscience letters488(2), 138–142. https://doi.org/10.1016/j.neulet.2010.11.016
  3. Yamanaka, K., Yamagata, B., Tomioka, H., Kawasaki, S., & Mimura, M. (2010). Transcranial magnetic stimulation of the parietal cortex facilitates spatial working memory: near-infrared spectroscopy study. Cerebral cortex (New York, N.Y. : 1991)20(5), 1037–1045. https://doi.org/10.1093/cercor/bhp163
  4. Boyd, L. A., & Linsdell, M. A. (2009). Excitatory repetitive transcranial magnetic stimulation to left dorsal premotor cortex enhances motor consolidation of new skills. BMC neuroscience10, 72. https://doi.org/10.1186/1471-2202-10-72
  5. Thakral, P., Madore, K., & Schacter, D. (2017). A role for the left angular gyrus in episodic simulation and memory. Journal of Neuroscience, 37(34), 8142-8149. https://doi.org/10.1523/jneurosci.1319-17.2017
  6. Luber, B. and Lisanby, S. H. (2014). Enhancement of human cognitive performance using transcranial magnetic stimulation (tms). NeuroImage, 85, 961-970. https://doi.org/10.1016/j.neuroimage.2013.06.007
  7. Thut, G., Veniero, D., Romei, V., Miniussi, C., Schyns, P. G., & Gross, J. (2011). Rhythmic tms causes local entrainment of natural oscillatory signatures. Current Biology, 21(14), 1176-1185. https://doi.org/10.1016/j.cub.2011.05.049
  8. Bestmann, S., Ruff, C. C., Blakemore, C., Driver, J., & Thilo, K. V. (2007). Spatial attention changes excitability of human visual cortex to direct stimulation. Current Biology, 17(2), 134-139. https://doi.org/10.1016/j.cub.2006.11.063
  9. Esterman, M., Thai, M., Okabe, H., DeGutis, J., Saad, E., Laganiere, S., … & Halko, M. A. (2017). Network-targeted cerebellar transcranial magnetic stimulation improves attentional control. NeuroImage, 156, 190-198. https://doi.org/10.1016/j.neuroimage.2017.05.011
  10. Riddle, J., Hwang, K., Cellier, D., Dhanani, S., & D’Esposito, M. (2019). Causal evidence for the role of neuronal oscillations in top–down and bottom–up attention. Journal of Cognitive Neuroscience, 31(5), 768-779. https://doi.org/10.1162/jocn_a_01376
  11. Ahrens, M., Veniero, D., Freund, I. M., Harvey, M., & Thut, G. (2019). Both dorsal and ventral attention network nodes are implicated in exogenously driven visuospatial anticipation. Cortex, 117, 168-181. https://doi.org/10.1016/j.cortex.2019.02.031

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