Monthly Archives: December 2015

Shared attention

Social interaction or communication requires the sharing of attention. If two people are not paying attention to one another then there is no interaction and no communication. Shared attention is essential for a child’s development of social cognition and communication skills. Two types of shared attention have been identified: mutual gaze when two people face one another and attend to each others eyes; and joint attention when two people look at a third person or object. Joint attention is not the same for both individuals because one initiates it and the other responds.

In a recent paper, researchers studied shared attention (Takahiko Koike etal; Neural substrates of shared attention as social memory: A hyperscanning functional magnetic resonance imaging study ; NeuroImage 125 (2016) 401–412). This cannot be done on an individual level as it involves social exchange and so the researchers used fMRI hyperscanning. Real time video recording and projection allowed two individuals in separate scanners to communicate through facial expression and eye movements while they were both being scanned. Previous studies had shown neural synchronization during shared attention and synchronization of eye blinks. They found that it was the task of establishing joint attention which requires sharing an attentional temporal window that task creates the blink synchrony. This synchrony is remembered in a pair specific way in social memory.

Mutual gaze is needed to give mutual attention - and that is needed to initiate joint attention which requires a certain synchrony - and finally that synchronizing results in a specific memory of the pair’s joint attention which allows further synchrony during subsequent mutual gaze without joint attention first.

Here is their abstract: “During a dyadic social interaction, two individuals can share visual attention through gaze, directed to each other (mutual gaze) or to a third person or an object (joint attention). Shared attention is fundamental to dyadic face- to-face interaction, but how attention is shared, retained, and neutrally represented in a pair-specific manner has not been well studied. Here, we conducted a two-day hyperscanning functional magnetic resonance imaging study in which pairs of participants performed a real-time mutual gaze task followed by a joint attention task on the first day, and mutual gaze tasks several days later. The joint attention task enhanced eye-blink synchronization, which is believed to be a behavioral index of shared attention. When the same participant pairs underwent mutual gaze without joint attention on the second day, enhanced eye-blink synchronization persisted, and this was positively correlated with inter-individual neural synchronization within the right inferior frontal gyrus. Neural synchronization was also positively correlated with enhanced eye-blink synchronization during the previous joint attention task session. Consistent with the Hebbian association hypothesis, the right inferior frontal gyrus had been activated both by initiating and responding to joint attention. These results indicate that shared attention is represented and retained by pair-specific neural synchronization that cannot be reduced to the individual level.

The right inferior gyrus (rightIFG) region of the brain has been linked in other research with: interfacing between self and other; unconscious incorporation of facial expression in self and others; the release from mutual attention; and, neural synchronization during social encounters. The rightIFG is active in both initiating and responding to joint attention and in the synchrony during mutual gaze (when it is present). However it is unlikely to cause blinking directly. “Neural synchronization of the right IFG represents learned shared attention. Considering that shared attention is to be understood as a complementary action due to its social salience, relevance in initiating communication, and joint action, the present finding is consistent with a previous study by Newman-Norlund et al. who showed that the right IFG is more active during complimentary as compared to imitative actions.” Communication, communication, communication!

This fits with the theory that words steer joint attention to things present or absent, concrete or abstract in a way that is similar to the eyes steering joint attention on concrete and present things. Language has harnessed the brain’s mechanisms for joint attention if this theory is correct (I think it is).

 

Close but not quite

I wonder how often we are almost right but not quite. It seems to be a fairly common trap in biology.

It has been thought for many years (140+ years) that the primary motor cortex (lying across the top of the head) mapped the muscles of the body and controlled their contractions. From this we got the comical homunculus with its huge lips and hands on a spindly little body. Each small area on this map was supposed to activate one muscle.

A recent paper by Graziano, Ethological Action Maps: A Paradigm Shift for the Motor Cortex (here), argues that this is not as it appears. What is being mapped are actions and not muscles. Here is the abstract:

The map of the body in the motor cortex is one of the most iconic images in neuroscience. The map, however, is not perfect. It contains overlaps, reversals, and fractures. The complex pattern suggests that a body plan is not the only organizing principle. Recently a second organizing principle was discovered: an action map. The motor cortex appears to contain functional zones, each of which emphasizes an ethologically relevant category of behavior. Some of these complex actions can be evoked by cortical stimulation. Although the findings were initially controversial, interest in the ethological action map has grown. Experiments on primates, mice, and rats have now confirmed and extended the earlier findings with a range of new methods.

Trends - For nearly 150 years, the motor cortex was described as a map of the body. Yet the body map is overlapping and fractured, suggesting that it is not the only organizing principle. In the past 15 years, a second fundamental organizing principle has been discovered: a map of complex, meaningful movements. Different zones in the motor cortex emphasize different actions from the natural movement repertoire of the animal. These complex actions combine multiple muscles and joints. The ‘action map’ organization has now been demonstrated in primates, prosimians, and rodents with various stimulation, lesion, and neuronal recording methods. The action map was initially controversial due to the use of electrical stimulation. The best argument that the action map is not an artifact of one technique is the growing confirming evidence from other techniques.”

Even settled science when it is neuroscience should be taken with a grain of salt. Any part of it could be something similar but not the same.

Powerful Induction

In an article in the Scientific American (here) Shermer points to ‘consilience of inductions’ or ‘convergence of evidence’. This is a principle that I have held for many, many years. Observations, theories and explanations are only trustworthy when they stop being a string of a few ‘facts’ and become a tissue or fabric of a great many independent ‘facts’.

I find it hard to take purely deductive arguments seriously – they are like rope bridges across a gap. They depend on every link in the argument and more importantly on the mooring points at either end. A causeway across the same gap does not depend on any single rock – it is dependable.

There is one theory that is put forward often and, to many, is ‘proven’, that is that brains can be duplicated with a computer. The reasoning goes something like: all computers are Turin machines, any program on a Turin machine can be duplicated on any other Turin machine, brains are computers and therefore Turin machines and can be duplicated on other computers. I see this as a very thin linear string of steps.

Step one is a somewhat circular argument in that being a Turin machine seems to be the definition of a ‘proper’ computer and so yes, all of those computers are Turin machines. What if there are other machines that do something that resembles computing but that are not Turin machines? Step two is pretty solid – unless someone disproves it which is unlikely but possible. The unlikely does happen; for example, someone did question the obvious ‘parallel lines do not meet’ to give us non-Euclidian geometry. Step three is the problem. Is the brain a computer in the sense of a Turin machine? People have said things like, “Well, brains do compute things so they are computers.” But no one has shown that any machine that can do any particular computation by any means is a Turin machine.

No one can say exactly how the brain does its thinking. But there are good reasons to question whether the brain does things step-wise using algorithms. In many ways the brain resembles an analog machine using massively parallel processing. The usual answer is that any processing method can be simulated on a digital algorithmic machine. There is a difference between duplication and simulation. No one says that a Turin machine can duplicate any other machine via a simulation. In fact, it is probable that this is not possible.

This is the sort of argument, a deductive one, that is hardly worth making. We will get somewhere with induction. It takes time: many experimental studies, methods have to be developed, models created and tested etc. But in the end it will be believable – we can trust that understanding because it is the product of a web or fabric of dependent inductions.

 

Rhythms - always rhythms

Why do we learn trigonometry in our school days and not get past the triangles and on to the waves? Who knows. But waves, rhythms and sine functions are such a constant part of this world. They are certainly important in biology.

We have seasonal rhythms, some of us have monthly rhythms, and we have circadian daily rhythms. Then we have heart rhythms, breathing rhythms, peristaltic gut waves and we have automatic muscle rhythms for walking and eye movements. We use rhythms in our speech, music, and dancing. Then there are the many brain wave patterns that we are only beginning to understand. The brain seems to function using rhythmic waves, waves of many frequencies, overlapping, synchronized and nested.

I noted a few things lately on this subject.

A paper in Cell, Descending Command Neurons in the Brainstem that Halt Locomotion, by J Bouvier and others (here), looks at the control of the start and stop of walking. The walking rhythm comes from an automatic network in the spinal cord but the commands to start and stop walking come from the brain stem. The question was about this signaling. There might be one signal with walking when it was present and not walking when it was absent. Or there could be two signals and this is what they found, separate on and off signals. The interesting thing from the stand point of rhythms is that a ‘stop’ signal was needed. Stopping a rhythm is not simple. The rhythmic dynamic of walking cannot be stop instantaneously to any point. There is no point that it can be just frozen that would leave a stable position with all feet on the ground and the center of gravity not off center. It takes a special functional network to stop the rhythm without stumbling, tripping or falling. Of course the rhythm could be just slowed until it stopped but most animals want to stop ‘on a dime’ rather than after some time.

In a release from UoW Madison (here) there is an outline of the work of J Samaha. He has found that our sight is controlled by the alpha rhythm in the back of the brain. We do not process the information that arrives from the eyes during the trough in the alpha rhythm but only during the peaks. The faster a persons alpha frequency, the more often they sample the world and the better they can distinguish close flashes of light as separate.

ScienceDaily has an item (here) about a paper by R Cho and others about the strengthening of synapses as we form associations during learning, memory and development.

Over the past 30 years, scientists have found that strong input to a postsynaptic cell causes it to traffic more receptors for neurotransmitters to its surface, amplifying the signal it receives from the presynaptic cell. This phenomenon, known as long-term potentiation (LTP), occurs following persistent, high-frequency stimulation of the synapse. Long-term depression (LTD), a weakening of the postsynaptic response caused by very low-frequency stimulation…Scientists have focused less on the presynaptic neuron’s role in plasticity, in part because it is more difficult to study”

Presynaptic cells occasionally release transmitters into the synapse when there is no activity in the cell as a whole and this was thought of as noise. They are called minis. Cho found that minis were not just random noise but they could also strengthen a synapse if they were delivered with a high frequency. “When we gave a strong activity pulse to these neurons, these mini events, which are normally very low-frequency, suddenly ramped up and they stayed elevated for several minutes before going down.” After a signal was transmitted, activity resembling an action potential continued without an actual signal. High frequency minis causes the synapse to strengthen, but low frequency ones do not.