Tag Archives: senses

Consciousness comes in “slices” roughly 400 milliseconds long

A new model proposed by EPFL scientists tries to explain how our brain processes information and then makes us consciously aware of it. According to their findings, consciousness forms as a series of short bursts of up to 400 milliseconds, with gaps of background, unconscious information processing in between.

Image via pixabay user johnhain

Subjectively, consciousness seems to be an uninterrupted state of thought and senses giving us a smooth image of the world around us. So to the best of our knowledge, sensory information is continuously recorded and fed into our perception; we then process it and become aware of it as this happens. We can clearly see the movement of objects, we hear sounds from start to end without pause, etc.

But have you ever found yourself reacting to something before actually becoming aware of the need to react? Let’s say you’re running and trip over, but you change your motions to prevent falling almost automatically. Or you’re in traffic, the car in front of you suddenly stops and you slam on the brakes instinctively, even before you realize the danger. If yes, you’ve most likely said “thanks reflexes” and left it like that.

This, however,  hints at processes that analyze data and elaborate responses without our conscious input, sparking a debate in the science community that goes back several centuries. Why does this automated response form — just as an extra safety measure? Or rather, because your consciousness isn’t always available when push comes to shove? In other words, is consciousness constant and uninterrupted, or more akin to a movie reel — a series of still shots?

Michael Herzog at EPFL and Frank Scharnowski at the University of Zurich now put forward a new model of how the brain processes unconscious information, suggesting that consciousness arises only in intervals up to 400 milliseconds, with no consciousness in between. By reviewing data from previously published psychological and behavioral experiments on the nature of consciousness — such as showing a participant several images in rapid succession and asking them to distinguish between them while monitoring their brain activity — they have developed a new conceptual framework of how it functions.

They propose a two-stage processing of information. During the first, unconscious stage, our brain processes specific features of objects such as color or shape. It then analyzes these objects with a very high time-resolution. But crucially to the proposed model, there is no actual perception of time during this phase — even time-dependent features such as duration or changes in color are not perceived as such. Time simply becomes a value assigned to each state, just as color or shape. In essence, during this stage your brain gathers and processes data, then puts them into a spreadsheet (a brainxcell if you will,) and “time” becomes just another value in a column.

Then comes the conscious stage: after unconscious processing is completed the brain renders all the features into our conscious thought. This produces the final picture, making us aware of the stimulus. Processing a stimulus to conscious perception can take up to 400 milliseconds, a considerable delay from a physiological point of view. The team focused their study on visual perception alone, and the delay might vary between the senses.

“The reason is that the brain wants to give you the best, clearest information it can, and this demands a substantial amount of time,” explains Michael Herzog. “There is no advantage in making you aware of its unconscious processing, because that would be immensely confusing.”

This is the first time a two-stage model has been proposed for how consciousness arises, and it may offer a more refined picture than the purely continuous or discrete models. It also provides useful insight into the way our brain processes time and relates it to our perception of the world.

The full paper, titled “Time Slices: What Is the Duration of a Percept?” has been published online in the journal PLOS Biology and can be read here.


Neuroscientists read the mind of a fruit fly

Do flies dream of flying sheep? We might soon have the answer to that question, as Northwestern University neuroscientists have developed a method that allows them to pinpoint communicating neurons in a living fly’s brain — effectively paving the way for mind-reading. Their mapping of specific neural connection patterns could provide insight into the computational processes that underlie the workings of the human brain.

Image via naturetrib

Neurons rely on points of communication known as synapses to share information. As crunching sensory data is a collective effort, involving a large number or neurons, synapses are a good indicator of a brain’s processing power — and they’re the focus of Northwestern’s study.

“Much of the brain’s computation happens at the level of synapses, where neurons are talking to each other,” said Marco Gallio, assistant professor of neurobiology in Northwestern’s Weinberg College of Arts and Sciences and lead scientist of the study. “Our technique gives us a window of opportunity to see which synapses were engaged in communication during a particular behavior or sensory experience. It is a unique retrospective label.”

The team chose Drosphila melanogaster (the common fruit fly) for the study, as the insect’s brain and its communication channels are well documented, but they ran into a little problem: it’s impossible to look at a fly’s brain under the microscope as it’s performing any kind of complex activity, so they had to come up with a solution.

Their answer was to use fluorescent molecules to mark neurons, focusing on the neural networks of three of the fly’s sensory systems — smell, sight and themrosensory system.

Starting with the gene for a green fluorescent protein found in jellyfish, they were able to genetically engineer three differently-colored proteins to serve as labels. Then, to make the molecules light up only when synapses started firing, they split the molecules in two and attached one half to the neuron sending and the other to the neuron receiving the information.

As the insect was exposed to sensory triggers or performed an activity, neurons would touch briefly to communicate and the now-whole molecules started lighting up the parts of the fly’s brain that were involved in processing the information or directing movement. Even better, the fluorescent signal persists for hours after the communication event, allowing researchers to study the brain’s activity after the fact, under a microscope.

“Our results show we can detect a specific pattern of activity between neurons in the brain, recording instantaneous exchanges between them as persistent signals that can later be visualized under a microscope,” Gallio said.

By “reading” the brains they could tell if a fly had been in either heat or cold (at least for 10 minutes) an entire hour after the sensory event had happened, for example. They also could see that exposure to the scent of a banana activated neural connections in the olfactory system that were different from those activated when the fly smelled jasmine.

“Different synapses are active during different behaviors, and we can see that in the same animal with our three distinct labels,” said Gallio.

This is the kind of new technology scientists discuss in the context of President Obama’s BRAIN (Brain Research Through Advancing Innovative Neurotechnologies) Initiative, Gallio said. Such a tool will help researchers better understand how brain circuits process information, and this knowledge then can be applied to humans.

Their paper, titled “Dynamic labelling of neural connections in multiple colours by trans-synaptic fluorescence complementation” has been published in the journal Nature Communications.




Touch and sight – more connected than previously thought

What you see may be very much related to what you’ve just felt. Even though we were taught at school that each sense is processed in another area of the brain it seems that this theory may be wrong and that there is a lot more to understand about the way human brain works.

As an example, a light ripple of pins moving up the fingertip tricked the subjects of a study into perceiving some lines moving on a screen as moving down, and the other way around. So, there is something going on.

Some recent studies have proved that the way our brain works –  in this case processes the most important senses – is far more complex than thought for decades. Firstly, it was discovered that hearing and seeing are related to each other, but now it seems that this is far from being the end of the story.

In order to take the theory even further, a trick of perception named aftereffect was used by scientists, a phenomenon that occurs for example when watching a waterfall. Staring at it for some time will eventually make one perceive the stationary rocks as moving up. This happens because the neurons which are in charge of the “down” get tired while the “up” ones are still fresh and create this impression.

But what interested the researchers was the aftereffect caused by the sense of touch. A small gadget of the size of a stamp made of 60 pins in rows was used throughout the study as the participants were asked to rest a finger on top of it. Some of the rows were raised at different times, thus creating a gentle prodding movement which was directed away or toward the person, for ten seconds. Then, the subjects were asked to look at a computer screen on which they could see common patterns of white and black horizontal lines. The lines were constantly moving and switching places, but their entire movement could be characterized as upward or downward.

Simple task, isn’t it? Well, not when the brain has a lot of stimuli to cope with. This is why the subjects who had felt the lines on the little device going up perceived the lines on the screen as going down and the other way around. This is the the visual aftereffect. A touch aftereffect can also be induced as watching lines going up on a screen made the participants feel the pins as going down.

Now it seems quite clear that sight and touch are connected to a larger extent than it was expected. Now, the next step is to find where exactly in the brain the connection is created.

source: Body & Brain

It’s a fact – humans can smell fear too!

Since early childhood we’ve been told that if we are afraid of a dog which has turned violent, our furry buddy will “smell” our fear and we will eventually end up bitten. Not the most comfortable feeling ever…but as long as only animals can do it…
Many species are known to release a chemical signal in order to warn other members of the family in case something dangerous occurs; however, a study conducted by Denise Chen from Rice University seems to prove that we can do the same thing too.
When perceiving the world we use all of our senses, some being more important in this process. What researchers wanted to know is how important perceiving fear is.
“Fearful sweat” was collected from several male volunteers who had been given gauze pads for their armpits before being shown videos dealing with subjects which are known to be scary.
After this stage of the study, female subjects were exposed to chemicals from “fear sweat” and then shown different faces which varied from happy to ambiguous and scared. They had to indicate whether the face was happy or fearful by pressing buttons.
The smell of fear made women interpret the faces mostly as fearful in the case of the ambiguous ones, but didn’t change the results if the faces were clearly happy.
In conclusion, emotions caused by a sense can influence the way the same emotion is perceived through another sense, but only if the signals are not clear.

All these show that human sweat is a clear indicator of emotions too, humans being able to sense them and thus be influenced by these signals, mostly if other senses cannot be used.

Other species of animals use smell as a main way of communication when marking their territories or sending a message regarding a possible danger. The way we perceive smells and especially how important it is to us still remains a mystery, a mystery which seems to find a few answers.
source: Rice University