Csmsdust

reading isn't enough I need to swallow the book whole

ok well im going to build a good future for myself whether i like it or not

Your whole room is a better mirror of you than the reflection in the mirror in your room.

Chaos Game -- from Wolfram MathWorld

mathworld.wolfram.com

Chaos Game -- from Wolfram MathWorld

An algorithm originally described by Barnsley in 1988. Pick a point at random inside a regular n-gon. Then draw the next point a fraction r

Special brain cells react to unexpected situations

New research from the Netherlands Institute for Neuroscience shows that chandelier cells, a specific type of brain cell, become active during unexpected situations. “Researchers have been wondering about the functionality of these cells for a long time”.

You’re cycling to work through the city and suddenly you see a new building somewhere. On the first day that is very surprising. On day 2 this diminishes somewhat, and after a week you no longer notice it at all. The same thing happens the other way around: when a building that was always there suddenly disappeared, you are also surprised. But how does your brain signal unexpected changes and which cells are involved?

To learn more about this phenomenon, Koen Seignette from Christiaan Levelt’s lab joined forces with his colleagues from the Kole lab and Roelfsema lab. Together, they investigated a special type of brain cell found in small numbers in the cortex: the chandelier cell. In contrast to other inhibitory brain cells, they only inhibit one spot of other cells, but there is remarkably little known about why and when.

New mouse model

Koen Seignette: ‘We already knew quite a lot about the function of most types of inhibitory brain cells, but chandelier cells were a mystery. This is because they are not clearly marked genetically, and so could not be properly examined. We have now obtained a mouse model in which the chandelier cells are fluorescently labeled. This allows us to image them live and determine when they are active. That offers new opportunities.’

‘As a first step, we looked at what chandelier cells in the visual cortex respond to. What happens to these cells when the mouse starts running or when we present visual stimuli? In one of the experiments we had the mice walk in a virtual tunnel. When the mouse ran, the tunnel moved, and when it stopped, so did the tunnel. Using this setup, we could create an unexpected situation by stopping the tunnel while the mouse was still running. It was during these events that the chandelier cells started firing like crazy.’

Plasticity

Christiaan Levelt: ‘We see that the type of stimulus does not actually matter that much, what matters is that it is unexpected and surprising. We also noticed that habituation and change occurs, comparable to the aforementioned example of the new building. At first the cells react strongly, but after repeated exposure the activity becomes weaker. This shows that the cells are able to adapt, which is a concept known as plasticity. This plasticity also occurs at a structural anatomical level: we can literally see changes in the synapses chandelier cells form on other brain cells.’

‘What makes this study important is that this is the first really comprehensive study of chandelier cells in the visual cortex. We have not only determined what they respond to, but also which brain cells they form connections with, and what their influence is on other brain cells. This has never been looked at in such detail before. Understanding the role of these inhibitory neurons in the cortex is crucial for many processes, including learning from unexpected circumstances. We all know that you remember things better when it really surprises you. If the prediction is incorrect, that’s where you can find the information. You need plasticity to update your insights, and these cells could play a role in that.’

Why are chandelier cells so special?

Chandelier cells, named for their resemblance to a chandelier, are inhibitory brain cells that focus on the starting point (axon initial segment) of electrical signals in the pyramidal cells, the most common cells in the cortex. It was thought that chandelier cells could exert strong control over pyramidal cells by blocking the action potential. Surprisingly, the current research shows that this effect is actually very weak, which contradicts previously drawn conclusions.

‘Wrinkles’ in time experience linked to heartbeat

How long is the present? The answer, Cornell researchers suggest in a new study, depends on your heart.

They found that our momentary perception of time is not continuous but may stretch or shrink with each heartbeat.

The research builds evidence that the heart is one of the brain’s important timekeepers and plays a fundamental role in our sense of time passing – an idea contemplated since ancient times, said Adam K. Anderson, professor in the Department of Psychology and in the College of Human Ecology (CHE).

“Time is a dimension of the universe and a core basis for our experience of self,” Anderson said. “Our research shows that the moment-to-moment experience of time is synchronized with, and changes with, the length of a heartbeat.”

Saeedeh Sadeghi, M.S. ’19, a doctoral student in the field of psychology, is the lead author of “Wrinkles in Subsecond Time Perception are Synchronized to the Heart,” published in the journal Psychophysiology. Anderson is a co-author with Eve De Rosa, the Mibs Martin Follett Professor in Human Ecology (CHE) and dean of faculty at Cornell, and Marc Wittmann, senior researcher at the Institute for Frontier Areas of Psychology and Mental Health in Germany.

Time perception typically has been tested over longer intervals, when research has shown that thoughts and emotions may distort our sense time, perhaps making it fly or crawl. Sadeghi and Anderson recently reported, for example, that crowding made a simulated train ride seem to pass more slowly.

Such findings, Anderson said, tend to reflect how we think about or estimate time, rather than our direct experience of it in the present moment.

To investigate that more direct experience, the researchers asked if our perception of time is related to physiological rhythms, focusing on natural variability in heart rates. The cardiac pacemaker “ticks” steadily on average, but each interval between beats is a tiny bit longer or shorter than the preceding one, like a second hand clicking at different intervals.

The team harnessed that variability in a novel experiment. Forty-five study participants – ages 18 to 21, with no history of heart trouble – were monitored with electrocardiography, or ECG, measuring heart electrical activity at millisecond resolution. The ECG was linked to a computer, which enabled brief tones lasting 80-180 milliseconds to be triggered by heartbeats. Study participants reported whether tones were longer or shorter relative to others.

The results revealed what the researchers called “temporal wrinkles.” When the heartbeat preceding a tone was shorter, the tone was perceived as longer. When the preceding heartbeat was longer, the sound’s duration seemed shorter.

“These observations systematically demonstrate that the cardiac dynamics, even within a few heartbeats, is related to the temporal decision-making process,” the authors wrote.

The study also showed the brain influencing the heart. After hearing tones, study participants focused attention on the sounds. That “orienting response” changed their heart rate, affecting their experience of time.

“The heartbeat is a rhythm that our brain is using to give us our sense of time passing,” Anderson said. “And that is not linear – it is constantly contracting and expanding.”

The scholars said the connection between time perception and the heart suggests our momentary perception of time is rooted in bioenergetics, helping the brain manage effort and resources based on changing body states including heart rate.

The research shows, Anderson said, that in subsecond intervals too brief for conscious thoughts or feelings, the heart regulates our experience of the present.

“Even at these moment-to-moment intervals, our sense of time is fluctuating,” he said. “A pure influence of the heart, from beat to beat, helps create a sense of time.”