Ultrasound technique modifies human reward learning for the first time

The nucleus accumbens is a tiny element of the human brain triggered when we experience something enjoyable, and used to help us learn behaviors that lead to rewards.

A new study has shown for the first time that its influence on human behavior can be altered using transcranial ultrasound stimulation (TUS).

Applying the technique for just over a minute at a time, researchers were able to influence how people learned the links between certain cues and rewards.

The result was that they were more likely to repeat a choice that had previously paid off, their learning rates following positive outcomes increased and they were more likely to make positive choices more quickly.

Up to this point, such outcomes have only been achieved through surgical procedures such as deep brain stimulation (DBS), which involves electrodes being directly attached to areas within a person's brain.

However, those involved in the current study say their findings could signal that TUS has the potential to be used as an equally beneficial – and non-invasive – alternative to help those impacted by neurological or psychiatric disorders including addictions, depression and eating disorders.

The study is published in the journal Nature Communications and was led by researchers from the University of Plymouth. It also involved the University of Oxford, John Radcliffe Hospital, University Hospitals Plymouth NHS Trust, Brown University, and the VA Providence Healthcare System.

Professor Elsa Fouragnan, Director of the Centre for Therapeutic Ultrasound and the Brain Research and Imaging Centre (BRIC) at the University of Plymouth, led the research. She said: "For decades, the nucleus accumbens has sat at the centre of theories of motivation and reinforcement learning. It is the hub where dopamine signals and limbic inputs converge to shape how strongly rewards pull our choices. We were able to pinpoint a clear link between a specific learning trait, tied to impulsivity, and a structure that until now could not be reached without surgery. The fact that we can now modulate this area non-invasively, and in a personalised manner, opens extraordinary possibilities for clinical translation."

The study forms part of ongoing and pioneering research taking place at the University of Plymouth into the benefits of TUS for conditions including anxiety and depression, addiction and other neurological or psychiatric disorders.

In this project, the researchers recruited 26 healthy participants who visited the BRIC facility four times – once to plan their TUS intervention, followed by three sessions where TUS was applied to different parts of their brain.

Roughly 10 minutes after the ultrasound intervention, participants were placed in the scanner to perform a series of tasks over the space of an hour while the research team monitored changes in their behaviour and brain activity.

The participants' performance in the tasks was also cross-checked against that of patients with bilateral deep brain stimulation electrodes targeted to the nucleus accumbens as part of therapies for treatment-resistant anorexia nervosa.

The results showed that while DBS often normalizes reward-seeking behaviour, TUS had an opposite and excitatory effect – however, both result in people's learning and reward sensitivity being altered.

This study is the most significant I have had the privilege to lead so far. We uncovered a clear link between a specific cognitive process and a deep-brain structure that, until now, was beyond reach without surgery. It marks a turning point for neurotechnology, showing that a non-invasive ultrasound approach can influence behaviour and may one day help restore mental balance."

Professor Elsa Fouragnan, Director of the Centre for Therapeutic Ultrasound and the Brain Research and Imaging Centre (BRIC), University of Plymouth