Tuesday, May 25, 2021

Synchrony and sociality observed in mouse brains [neuroscience beyond the individual]

Virginia Hughes, Scientists Drove Mice to Bond by Zapping Their Brains With Light, The NYTimes, May 25, 2021.

Late one evening last March, just before the coronavirus pandemic shut down the country, Mingzheng Wu, a graduate student at Northwestern University, plopped two male mice into a cage and watched as they explored their modest new digs: sniffing, digging, fighting a little.

With a few clicks on a nearby computer, Mr. Wu then switched on a blue light implanted in the front of each animal’s brain. That light activated a tiny piece of cortex, spurring neurons there to fire.

Mr. Wu zapped the two mice at the same time and at the same rapid frequency — putting that portion of their brains quite literally in sync. Within a minute or two, any animus between the two creatures seemed to disappear, and they clung to each other like long-lost friends.

“After a few minutes, we saw that those animals actually stayed together, and one animal was grooming the other,” said Mr. Wu, who works in the neurobiology lab of Yevgenia Kozorovitskiy.

Mr. Wu and his colleagues then repeated the experiment, but zapped each animal’s cortex at frequencies different from the other’s. This time, the mice displayed far less of an urge to bond.

Research originally reported in an article in Nature Neuroscience.

Beyond individual brains:

For centuries, she noted, most neuroscientists have been focused on the individual brain and the function of its various parts. “The whole field is built on looking at a brain in a jar — Where’s memory? Where’s vision?” Dr. Wheatley said. But to understand nuanced social behaviors, which by definition can’t be observed in isolation, “it’s very important that we’re beginning to look at more than one brain at the same time.”

The new study also raises questions about a tantalizing phenomenon that has been observed in humans for decades, with potential implications for everything from social anxiety disorders to pandemic isolation: When two people interact, their brain patterns align in intriguing ways.

Is there something here not?

The results may suggest that brain synchrony is a causal driver of social behavior — and is more than just a byproduct of brains performing similar activities, or thinking similar thoughts, in a shared environment.

But many more experiments will be needed before scientists can reach that conclusion with confidence. Almost all of the data in people, too, is ambiguous: Neural synchrony seems to be tightly linked with behavior, but that doesn’t mean it is the root cause. That uncertainty has led many researchers to wonder whether synchrony really matters.

“There is an overwhelming amount of evidence that we synchronize our behaviors and physiological rhythms spontaneously, and when we do so, we cooperate more and like each other better,” said Ivana Konvalinka, a cognitive scientist at the Technical University of Denmark who studies two-person neuroscience. But, she said, “despite working within this field, I am still not entirely convinced that the fact that our brains sync up has any functional significance at all.”

Yes, there's something there, but thinking of it as a "a causal driver of social behavior" is probably not a useful framing. It would be more useful to thinking of mutual sync as facilitating a class of behavioral modes. See my various posts about synchrony for more.

H/t Tyler Cowen.

A better way to think about the significance of interaction syncchronization

As I've indicated, I believe that looking at synchrony as "a causal driver of social behavior" is not the way to do it. Here's a passage from an essay-review I did some years ago of Steven Mithen, The Singing Neaderthals (2005) that suggests a different conceptual approach:

Consider an observation that Mithen offers early in his book (p. 17). He cites work by Peter Auer who, along with his colleagues, has analyzed the temporal structure of conversation. They discovered that, when a conversation starts, the first speaker establishes a rhythm to which the other speakers time their turn-taking. That is, even though they are only listening, other parties are actively attuned to the rhythm of the speaker’s utterance (cf. Condon 1986). What if this were necessary to conversation, and not just an incidental feature of it?

Let us recall some passages from Eric Lenneberg’s landmark review and synthesis, The Biological Foundations of Language (1967). While he does not address the issue of conversational turn-taking, he does devote the better part of chapter three to timing issues. He was particularly interested in problems arising from the fact that neural impulses travel relatively slowly and that the recurrent nerve, innervating the larynx, is over three times as long as the trigeminal branch innervating the one of the jaw muscles. It also has a smaller diameter, which means that impulses travel more slowly in it than in the trigeminal. The upshot, observes Lenneberg, is that “innervation time for intrinsic laryngeal muscles may easily be up to 30 msec longer than innervation time for muscles in and around the oral cavity.” He goes on to observe: “Considering now that some articulatory events may last as short a period as 20 mesc, it becomes a reasonable assumption that the firing order in the brain stem may at times be different from the order of events at the periphery” (96). It is on the basis of such considerations, which he discusses in some detail, that Lenneberg concludes: “rhythm is … the timing mechanism which should make the ordering phenomenon physically possible” (119).

It follows from this that, if you wish your utterances to smoothly intercalate with those of others, you need to share their rhythms; that is the only way your conversational entrances will be appropriately timed. Still, this might merely be a conversational convenience, not a necessity. So, let us consider the problem of speech perception.

We know that, while we tend to hear speech as a string of discrete sounds, that is something of an illusion. Sonograms do not show the segmentation that we hear so easily (Lenneberg 93-94). The brain is doing some sophisticated analysis of the sound stream. Though I am not aware that anyone has investigated this, I can imagine that it would be very useful if the listener operated within the same temporal framework as the speaker. This might help with the segmentation. If this is so, rhythmic synchronization is no longer simply a feature of how the nervous system happens to operate. It becomes essential to being able to treat the speech stream as a string of phonemes; it is necessary to linguistic communication.

Let us push the argument a step further. For the last decade or so there has been considerable interest in the notion that people acquire a so-called theory of mind (TOM) early in maturation and that this TOM is critical to interpersonal interaction (see e.g. Baron-Cohen 1995). Gaze following is one behavior implicated in TOM. Humans beyond a relatively early age will follow the direction of one another's gaze. I would like to suggest that we notice gaze direction in people with whom we synchronize, but not otherwise.

Think about the perceptual requirements of noticing and tracking gaze direction. Even at conversational distance, another person’s eyes are small in relation to the whole visual scene; thus the visual cues for gaze direction will also be small. Further, people in conversation are likely to be in constant relative motion with respect to one another. The motions may not be large – head turns and gestures, trunk motion – but they will be compounded by the fact that one’s eyes are in constant saccadic motion. Synchronization would eliminate one component of relative motion between people and therefore simplify the process of picking up the minute cues signalling gaze direction. But if one cannot properly synchronize with others, then those cues will be more difficult to notice and track. Thus the capacity for interpersonal synchrony may be a prerequisite for the proper functioning of TOM circuitry.

That's the key, eliminating one component of relative motion between individuals, people in one case, mice in another. Mice are small and their vision is not that acute. They need all the help they can get in perceiving one another, especially when both are in motion. What kind of causal role is this? It simplifies mutual perception. 

Driver isn't the concept we want. It's a coordinator. Driver has the wrong connotations. It suggests something that is behind, pushing the interaction forward. That's not what's going on. It's simplifying the channel through which interaction takes place.


  1. Condon called interactional synchrony "the dance." Much of human development could be viewed as learning self synchrony inside a culture. Is culture about such dancing?
    As I read your article today the birds are singing at dawn. Are they synchronizing some aspect of behavior? Much of bird flight in flocks grossly appears remarkably synchronous. Condon's quiet work half a century ago remains astonishingly prescient today.