Scientists have used ultrasound waves to control the brains of monkeys, which they say could lead to a treatment for addiction or depression in humans.
In experiments, US researchers directed pulses of ultrasound waves at the brains of macaque monkeys to control their decision-making.
By pointing the waves at parts of the frontal cortex, they could influence whether the creatures selected one of two targets during a computerised selection task.
If applied to humans, pain-free ultrasound brain stimulation could treat decision-making disorders, including addiction and binge eating, in place of drugs or surgery.
The treatment also has potential to treat mental disorders such as depression and anxiety or neurological disorders like chronic pain and epilepsy.
Non-invasive pulses of ultrasound waves aimed at specific regions in the brains of macaque monkeys can give some control over the monkeys’ choices
‘Brain disorders should be treated in targeted and personalised ways instead of offering patients cocktails of drugs,’ said Jan Kubanek, assistant professor of biomedical engineering at the University of Utah.
‘But to do that, we need a tool that provides non-invasive, precise, and personalised treatments to address the source of the problem in each individual.
‘This up until now has only been a dream.’
Ultrasonic waves for precision therapy involves pulses of sound at a high, inaudible frequency, aimed into the brain using an ultrasonic transducer, similar to wands used for ultrasound scans.
The sound pulses target neural circuits in the brain, activating neurons and influencing the behaviour that those neurons control.
Ultrasound waves – high frequency sound waves – have already been used to stimulate neurons, or nerve cells, of the brain.
Previous research has shown that low-intensity ultrasound waves applied to rodent brains from outside the head can stimulate neurons and cause muscle movements elsewhere in the body.
However, more recent studies have yielded less definitive results, suggesting the technique may have little or no effect.
Effects of ultrasound on behaviour in larger animals and humans, as opposed to rodents, has also not been well studied, according to the researchers.
To learn more, Professor Kubanek and colleagues engaged two macaque monkeys in an experiment already widely used to investigate choice behaviours.
The monkeys looked at a virtual target at the centre of a computer screen and were then presented with targets on the left and right sides of the screen, one very shortly after the other.
Monkeys used in such an experiment would naturally choose to look at the target that appears first on the screen.
However, by briefly applying ultrasonic waves to the monkeys’ frontal eye fields (FEF) – brain regions that control eye movement – the researchers found they could influence which target the monkey looked at.
Approximate location of the FEF (frontal eye fields) in humans
In primate brains, the FEF are located in the frontal cortex – the largest of the four major lobes of the brain – and play a role in visual attention and eye movements.
Just as each hemisphere controls muscles and glands on the opposite side of the body, when the researchers targeted the left FEF, the monkeys were more likely to look to the right target, they found.
Likewise, stimulation of the right FEF regions meant the monkeys chose the left target more often over the course of the experiments.
No effects were observed when ultrasound was applied to the motor cortex, which is involved in voluntary movements but not perceptual decision-making.
To test their behaviour further, the scientists then rewarded the monkeys differently for the same task.
‘Monkey A’ was rewarded with juice for selecting either target, whereas ‘Monkey B’ was only rewarded for selecting the first target.
However, the researchers were still able to control both monkeys’ choices, regardless of the potential reward on offer that may have influenced their decisions.
By briefly applying ultrasonic waves to the monkeys’ frontal eye fields (FEF), researchers influenced which target the monkey looked at. When the researchers targeted the left FEF, the monkeys were more likely to choose the right target, and vice versa
Even though a reward was on offer for Monkey B if it selected the first target, the ultrasound waves were still able to control its ultimate decision to select the second target.
The team say their ‘neuro-intervention’ can be used to identify which brain regions are involved in particular symptoms of diseases or behavioural conditions.
‘The paper shows that ultrasound can produce strong effects, up to the point of influencing behaviour,’ said Professor Kubanek.
‘And changes in behaviour is what we ultimately care about – for instance, we may be able to correct poor decision-making or at least reduce a person’s tremor in the hand.’
Kubanek says his team has built a prototype device to perform these treatments in human patients – in particular, he plans to begin first clinical trials in patients with major depression in three years’ time.
The study also provides recommendations for future applications of ‘ultrasonic neuromodulation’ in animals and humans.
This includes avoiding anaesthesia and applying stimulation relatively infrequently, as repetition appears to diminish the effects, the team said.
The research has been published in Science Advances.
WHAT IS A NEURON AND HOW DOES IT WORK?
A neuron, also known as nerve cell, is an electrically excitable cell that takes up, processes and transmits information through electrical and chemical signals. It is one of the basic elements of the nervous system.
In order that a human being can react to his environment, neurons transport stimuli.
The stimulation, for example the burning of the finger at a candle flame, is transported by the ascending neurons to the central nervous system and in return, the descending neurons stimulate the arm in order to remove the finger from the candle.
A typical neuron is divided into three parts: the cell body, the dendrites and the axon. The cell body, the centre of the neuron, extends its processes called the axon and the dendrites to other cells.Dendrites typically branch profusely, getting thinner with each branching. The axon is thin but can reach enormous distances.
To make a comparable scale, the diameter of a neuron is about the tenth size of the diameter of a human hair.
All neurons are electrically excitable. The electrical impulse mostly arrives on the dendrites, gets processed into the cell body to then move along the axon.
On its all length an axon functions merely as an electric cable, simply transmitting the signal.
Once the electrical reaches the end of the axon, at the synapses, things get a little more complex.
The key to neural function is the synaptic signalling process, which is partly electrical and partly chemical.
Once the electrical signal reaches the synapse, a special molecule called neurotransmitter is released by the neuron.
This neurotransmitter will then stimulate the second neuron, triggering a new wave of electrical impulse, repeating the mechanism described above.