Could the desire to drink that glass of wine or beer in the evening be linked to our brain's immune system?

In a first-of-its-kind study using mice, researchers have been able to switch off the impulse to drink alcohol by giving mice a drug that blocks a specific response from the immune system in the brain.

"Alcohol is the world's most commonly consumed drug, and there is a greater need than ever to understand the biological mechanisms that drive our need to drink alcohol," lead author and University of Adelaide PhD student Jon Jacobsen explained.

"Our body's circadian rhythms affect the 'reward' signals we receive in the brain from drug-related behaviour, and the peak time for this reward typically occurs during the evening, or dark phase.

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"We wanted to test what the role of the brain's immune system might have on that reward, and whether or not we could switch it off."

The researchers focused their attention on the immune receptor TLR4 and administered the drug Naltrexone, which is known to block TLR4.

"Our studies showed a significant reduction in alcohol drinking behaviour by mice that had been given Naltrexone, specifically at night time when the reward for drug-related behaviour is usually at its greatest," Jacobsen said.

"We concluded that blocking a specific part of the brain's immune system did in fact substantially decrease the motivation of mice to drink alcohol in the evening."

Senior author Professor Mark Hutchinson said there was a need to understand the implications for we humans.

"Given the drinking culture that exists in many nations around the world, including Australia, with associated addiction to alcohol and related health and societal issues, we hope our findings will lead to further studies."

The dinosaur-eating frog

The South American horned frog - dubbed the Pacman frog - has tremendous bite force. Photo / Kristopher Lappin
The South American horned frog - dubbed the Pacman frog - has tremendous bite force. Photo / Kristopher Lappin

Scientists say that a large, now extinct, frog called Beelzebufo and which lived about 68 million years ago in Madagascar would have been capable of eating small dinosaurs.

The conclusion comes from a new study of the bite force of South American horned frogs from the living genus Ceratophrys, known as Pacman frogs for their characteristic round shape and large mouth, similar to the video game character Pac-Man.

Due to their attractive body colouring, voracious appetite, and comically huge heads, horned frogs are very popular in the international pet trade.

The international team behind the study found that living large South American horned frogs have similar bite forces to those of mammalian predators.

"Unlike the vast majority of frogs which have weak jaws and typically consume small prey, horned frogs ambush animals as large as themselves - including other frogs, snakes, and rodents," said author Dr Marc Jones, of the University of Adelaide.

The study found that small horned frogs, with head width of about 4.5cm, could bite with a force of 30 newtons (N) - or about 3kg.

A scaling experiment, comparing bite force with head and body size, calculated that large horned frogs found in the tropical and subtropical moist lowland forests of South America, with a head width of up to 10cm, would have a bite force of almost 500 N.

This was comparable to reptiles and mammals with a similar head size.

"This would feel like having 50 litres of water balanced on your fingertip," said author Professor Kristopher Lappin, of California State Polytechnic University.

Based on their scaling relationship, the scientists estimated the bite force of the giant extinct frog Beelzebufo - which was in many ways similar to living horned frogs - may have had a bite up to 2200N, comparable to formidable mammalian predators such as wolves and female tigers.

At this bite force, Beelzebufo would have been capable of subduing the small and juvenile dinosaurs that shared its environment.

"This is the first time bite force has been measured in a frog," Lappin said.

"And, speaking from experience, horned frogs have quite an impressive bite, and they tend not to let go.

"The bite of a large Beelzebufo would have been remarkable, definitely not something I would want to experience firsthand."

How our neurons register familiar faces

Seeing a familiar famous face - like that of tennis star Roger Federer - lights up certain neurons in our brains, scientists say. Photo / File
Seeing a familiar famous face - like that of tennis star Roger Federer - lights up certain neurons in our brains, scientists say. Photo / File

When people see an image of a person they recognise - tennis star Roger Federer, for instance - particular cells light up in the brain.

Now, researchers have found that those cells light up even when a person sees a familiar face or object but fails to notice it.

The only difference, in that case, is that the neural activity is weaker and delayed in comparison to what happens when an observer consciously registers and can recall having seen a particular image.

The findings offer new insight into the nature of conscious perception.

"Our study finds that a 'Roger Federer cell' can also become active when its owner fails to notice the image of Roger Federer rapidly flickering by in a stream of other images," said Professor Florian Mormann, of Germany's University of Bonn Medical Centre.

"Thus, we find that there is highly abstract information present in neuronal activity that is inaccessible to conscious experience."

The researchers made the discovery by recording the activity of 2,735 individual neurons in 21 neurosurgical patients implanted with brain electrodes for epilepsy monitoring.

They took advantage of a phenomenon known as attentional blink in which people who attend to two familiar images in quick succession will often fail to notice the second.

The experimental setup allowed the researchers to directly compare the neural response to seen and unseen presentations of the very same image.

As expected, study participants often failed to notice the presence of a second target image, especially when it was presented soon after a first target image.

The researchers found that the corresponding neurons fired either way.

However, there was an observable difference in the strength and timing of that neural response.

"Studying the activity of individual neurons in awake, behaving humans was key to picking up weak but informative signals from individual neurons during nonconscious perception, particularly in regions further down the processing stream, which are impossible to measure with conventional tools," Mormann said.

"We were quite surprised to see that timing of neuronal responses is indicative of whether participants report having seen the image or not.

"The findings weighed in on theoretical debates about the nature of human consciousness.

For instance, it hadn't been clear whether consciousness was an all-or-nothing phenomenon or a matter of degrees.

The researchers say the observation that neuronal firing occurred in both cases, but differently, argued in favour of consciousness as a more nuanced, graded phenomenon.

The researchers say they'd now like to explore how the activity of individual neurons in one part of the brain is related to activity in other brain areas and how those connections relate to conscious awareness.