In new research published in Psychological Medicine, a team of scientists explored the effects of cortical paired associative stimulation, a form of transcranial magnetic stimulation (TMS), on enhancing the brain’s ability to resist alcohol-related impulses. Their findings revealed that while cPAS effectively strengthened the brain networks responsible for inhibiting responses in healthy adults, individuals with chronic alcohol use did not exhibit the same improvements. This suggests a unique brain response among those with alcohol use disorder, potentially tied to long-standing alterations in brain function due to alcohol consumption.
Cortical paired associative stimulation (cPAS) represents a pioneering approach in the field of neuromodulation. The essence of cPAS lies in its ability to deliver paired magnetic pulses to specific regions of the cortex, aiming to strengthen neuronal connections. This targeted stimulation seeks to enhance or restore the functional integrity of neural networks, particularly those implicated in cognitive processes such as impulse control.
Alcohol use disorder (AUD) is a medical condition characterized by an impaired ability to stop or control alcohol use despite adverse social, occupational, or health consequences. It is a complex brain disorder that can range from mild to severe and is marked by compulsive alcohol use, loss of control over alcohol intake, and a negative emotional state when not using alcohol.
Chronic alcohol consumption associated with AUD leads to neuroadaptive changes in the brain, particularly affecting the fronto-striatal pathways that are crucial for impulse control and decision-making processes. By employing cPAS, the researchers aimed to investigate whether stimulating specific brain areas involved in impulse control could ameliorate the ability to inhibit responses.
“Our work in Professor Valerie Voon’s Interventional Neuropsychiatry Group at the University of Cambridge is driven by the critical link between impulse control and addiction disorders such as alcohol use disorder,” explained study author Samantha N. Sallie, a PhD candidate in the Department of Psychiatry at the University of Cambridge.
“The COVID-19 pandemic has intensified societal challenges related to AUD and highlighted the need for effective treatments, propelling our search for innovative interventions that utilize the brain’s natural learning processes, such as synaptic plasticity. This approach is crucial because it addresses how changes in the brain’s synapses can sustain AUD by potentiating the brain’s reward system, leading to cravings that can trigger relapse.”
“Individuals with AUD often show impairments in response inhibition, the ability to stop or alter non-beneficial actions, such as succumbing to a craving,” Sallie said. “This impairment is not only a predictor of treatment outcomes but also a potential therapeutic target.
“The conserved neural network underlying response inhibition across species suggests that brain stimulation could enhance this control mechanism, offering new avenues for improving AUD treatment outcomes. Our interest lies in leveraging this potential to develop more effective strategies for managing AUD.”
The study included 55 participants from the greater Cambridgeshire area in the United Kingdom. This cohort comprised 20 individuals meeting the criteria for AUD, as defined by the Diagnostic and Statistical Manual of Mental Disorders Fifth Edition (DSM-5), and 35 healthy controls.
The heart of the study’s methodology revolved around the application of cPAS and the measurement of its effects on response inhibition, assessed via the Stop Signal Task (SST). For cPAS, the researchers targeted the right inferior frontal cortex (rIFC) and the right presupplementary motor area (pre-SMA), regions implicated in the brain’s inhibitory control network. The SST, a well-established experimental paradigm, required participants to make quick responses to visual cues while occasionally withholding their response when a stop signal appeared.
The study’s design included a single-blind between-subjects approach, with two cPAS sessions delivered in randomized order and at least 7 days apart to prevent carryover effects. Prior to the cPAS intervention, participants completed baseline self-report measures, adding a layer of subjective data to complement the objective SST findings.
In healthy control participants, cPAS demonstrated a clear beneficial effect on inhibitory control. Specifically, after undergoing cPAS, these individuals showed a significant improvement in their ability to inhibit responses, indicated by a reduction in stop signal reaction time. This finding suggests that cPAS effectively strengthened the fronto-striatal network, enhancing the brain’s capacity for response inhibition.
Contrastingly, participants with AUD did not exhibit the same improvement in response inhibition following cPAS. Despite receiving the same intervention, the AUD group showed no significant change in stop signal reaction time.
This lack of improvement suggests that chronic alcohol use may alter the brain’s responsiveness to neuromodulation interventions such as cPAS, possibly due to neuroadaptive changes induced by prolonged alcohol exposure. These changes could affect the brain’s neuroplasticity mechanisms, making it less receptive to the beneficial effects of cPAS on inhibitory control.
“Our findings suggest that cPAS, a novel, non-invasive brain stimulation technique, holds promise for enhancing response inhibition by reinforcing this critical brain network, as evidenced in healthy adults,” Sallie told PsyPost. “However, our research indicates that individuals with AUD may not experience the same benefits, likely due to the unique neural changes associated with long-term alcohol use. This insight opens up exciting possibilities for customizing brain stimulation approaches to meet the specific needs of those with AUD, potentially offering new pathways to support their recovery and decision-making processes.”
“One aspect of our findings that stood out was the varied response to cPAS within our AUD cohort,” Sallie added. “While the majority did not show improvement in response inhibition, a small subgroup of five individuals exhibited significant enhancements.”
“This unexpected variation highlights the complexity of AUD and suggests that factors such as individual differences in brain plasticity, the severity and duration of AUD, cognitive reserve, the integrity of neural pathways, or even lifestyle or environmental influences could play significant roles. Unfortunately, the limited number of participants showing this improvement restricted our ability to delve deeply into these factors, but it certainly unveils intriguing avenues for future research.”
Despite its promising insights, the study includes some limitations, including its relatively small sample size and the reliance on self-reported measures of alcohol consumption. These factors underline the need for further studies with larger cohorts and objective physiological measures to validate and extend these findings.
“Our study faced certain limitations, notably the reliance on a relatively small group of patients selected through convenience sampling,” Sallie said. “These individuals were drawn from a hepatology clinic, indicating they were dealing with significant health challenges related to AUD. The group presented a diverse range of addiction histories and stages of sobriety, including some who were still actively struggling with their addiction.”
“Importantly, we were able to demonstrate that the outcomes of our study were not merely the result of ongoing alcohol consumption. However, it is crucial to note that our approach did not include physiological measures to track alcohol or other substance use directly. Instead, we depended on self-reported information from the patients, which can sometimes introduce biases.”
Looking ahead, the researchers are poised to delve deeper into this line of inquiry, aiming to replicate their findings in a larger, more diverse cohort. The ultimate goal is to understand the nuances of brain response to cPAS in AUD and to explore combined therapies that could potentially enhance treatment outcomes for individuals grappling with addiction.
“Acknowledging the constraints posed by the small sample size in our study, we aim to replicate these findings in a larger, more well-characterized group of participants,” Sallie explained. “Our long-term objectives include not only confirming the initial results but also delving deeper into the mechanisms underlying the effectiveness of this brain stimulation intervention. Furthermore, we are interested in exploring how various factors influence the success of these interventions and whether combining them with existing pharmacotherapies could further improve response inhibition and clinical outcomes for individuals with AUD.”
The study, “Cortical paired associative stimulation shows impaired plasticity of inhibition networks as a function of chronic alcohol use,” was authored by Samantha N. Sallie, Saurabh Sonkusare, Alekhya Mandali, Violeta Casero, Hailun Cui, Natalie V. Guzman, Michael Allison, and Valerie Voon.
