Researcher explains how neurons see

Don’t feel too bad if you don’t have a clue how your brain works. After all, scientists, whose business it is to know about such things, admit that they are in the beginning stages of this study. They start by taking “simple” processes, in the hopes that these will throw light on the more complicated workings of our minds.


Scientist David Fitzpatrick, who was named CEO of Max Planck’s Jupiter campus in December, heads up the institute’s Functional Architecture and Development of Visual Cortex department. Recently, Fitzpatrick shared with us an inside look at his work and of one of the research projects he oversees.

In the process, he used an analogy, comparing the circuity in the human brain to computer circuitry, and also, by waving his arms around, explained that thanks to specific neurons in our brain, we are able to see that motion.

Wow. That gives a whole new definition to the term, “being wired.”

So, to start: Max Planck Florida Institute is a basic research society.

“The Florida institute is focused on the brain,” Fitzpatrick said. “Specifically, we are exploring neural circuits, the complex synaptic networks of the brain. We want to understand how they are organized, how they function, and how they develop. This requires bringing together scientists with expertise in different levels of analysis — genetic, molecular, cellular, circuit and behavioral — and developing new technologies that make cutting-edge scientific discoveries possible.”

Brain circuits are the synaptic networks of neurons that interact to create movement, perception, thought, memory and emotions. You can think of them this way, he said.

Network of neurons

“The brain is an incredibly complex biological computer, and neural circuits are like what’s running inside your computer,” he said. “The circuits that make the computer able to register the keys that are being pushed, that’s the sensory side. And the output, that’s what pops up on the screen. We want to understand how the circuits work, how they transform sensory input into a motor output and how these circuits are constructed during development. This information is critical for understanding a wide range of brain disorders.”

One area that is of particular interest to the scientists in Fitzpatrick’s lab is the role that experience plays in the development of neural circuits. Most of the synapses (the connections between neurons) in the cerebral cortex (the outer portion of the brain that’s responsible for movement, perception, thought and memory) are formed at a time when experience can influence their formation.

“After birth, there’s a huge increase in the density of synapses in the cortex, and we now know that patterns of neural activity driven by experience with the outside world influences how these circuits form,” Fitzpatrick said. “We are interested in understanding how that comes about. How is it that experience can influence the formation of these circuits?”

This is an important issue to address considering that there are many neuro-developmental disorders, the most well-known being autism. These disorders are likely to reflect alterations in the way that experience influences the development of neural circuits.

The visual cortex is used as a model system to explore these questions in his lab, he said, because it’s an easy system to manipulate. Scientists can control the visual information coming in, and they can ask how visual information influences the formation of circuits.

“We have been studying a property in the visual cortex that emerges with experience, and this property is known as selectivity for direction of motion,” he said. “If I wave my arm, you see my hand move in a certain direction. The reason that you are able to recognize its direction of motion is because you have neurons in your cerebral cortex that are sensitive to movement in a certain direction. Some neurons are sensitive to movement upwards, others to movement downwards, left and right. Our research has shown that the selective responses of cortical neurons to motion direction is acquired through experience with visual motion at an early stage in development.”

How are we able to “see” movement?
Specific neurons in the brain are sensitive to different  directions of motion.
Have to wonder how excited those neurons must get when “faced” with all these opposing directions.

What the scientists don’t understand is the mechanism responsible for that, he said.

“We don’t understand which parts of the neural circuits that make up the cerebral cortex are being altered by visual experience, and how these alterations generate direction selectivity,” he said. “But we think that if we can understand the mechanisms that are responsible for building up this response property, we will have a better understanding of the fundamental mechanisms by which experience influences the formation of neural circuits. We are interested in how it is that neural circuits get built and how our interaction with the world around us influences the construction of these circuits.”

Progress all comes down to the tools that the scientists have to address these questions.

“And in the last five years, there’s been an explosion of new techniques that are allowing us to visualize circuits in the brain and control their activity with light in ways that we couldn’t have dreamed of,” Fitzpatrick said. “So quite literally, we can visualize neurons in living brains, we can visualize their structure, and we can visualize their activity.”

To explain, “activity,” he said that neurons communicate with each other through synapses and the synapse involves a chemical transmission from one neuron to another, but the basic mode of communication is electrical. So a neuron generates an electrical signal that travels down its axon where it reaches a synapse, releases a neurotransmitter, and that neurotransmitter causes an electrical event in the dendrite, the receiving part, of the next neuron.

He gives an idea of some of the complexity: “One neuron in the cerebral cortex receives between 5,000 to 12,000 synapses onto its dendrite, and it is the specificity in the patterns of connections between neurons that is responsible for selectivity in neuronal responses, such as selectivity for direction of motion. We are still far from understanding the ‘wiring diagram’ that defines cortical circuits and how experience influences the patterns of connections that form between different neurons. This is what we are after.”

Back to the tools, with the newest technologies, scientists are now in the position to use light to see the neuron and its connections in a living brain, to visualize the activity in the neuron, and even to control its activity.

“We are developing a powerful set of tools for ‘interrogating’ neural circuit function,” he said. Their goal, he explained, “is to be able to really understand the structure of the neurons, the way the synapses are arranged, and the way in which experience shapes those connections.”

So, the scientists can go into the brain and control the activity of neurons and see how controlling their activity impacts the response of the neuron to motion selectivity, he said.

“Using these new techniques, we can begin to understand how all the inputs that come into a neuron contribute to its function,” he said.

Based on the idea that neuro-development disorders reflect alterations in how experience builds circuits, if the scientists can understand the basic mechanism through which experience builds circuits, than they can begin to understand these disorders.

“I mentioned autism, because it emerges as the child develops, it’s very profound, and increasing in terms of the number of people impacted,” he said. “Children appear to be normal and then begin to exhibit the symptoms of autism. It’s very likely that what’s going on here is some alteration in the way experience shapes the development of brain circuits.”

To be clear, Fitzpatrick addressed a problem faced by basic scientists: “People need to appreciate that we still know very little about neural circuits and the mechanisms that are responsible for their development. Even with the discoveries that these new techniques are making possible, the complexities of the brain make translating this knowledge into effective treatments a difficult process.

“But, it’s fundamental, basic science research that holds the key to understanding the normal mechanisms of brain development, and it’s that information that ultimately is crucial for in understanding disorders that reflect alterations in normal circuit development,” he said.

The scientists literally are going to the basics and asking: What are these circuits? They are saying: Let’s define them. Let’s map out what the circuits are and understand how these circuits produce this remarkable degree of selectivity.

The work in Fitzpatrick’s lab addresses a relatively simple question:  How is it that neurons in the brain respond selectively to the direction of a moving stimulus?

“We are not talking about how the brain represents thoughts or emotions,” he said. “These are much more complicated issues. But if we can take something simple — how do neuron circuits represent the direction of a moving stimulus, if we can understand how that happens, and how experience with moving stimuli builds that representation, then we can take what we learn and apply it to these other, far more complicated processes.”

written for palm2jupiter

Here is a link to a video presentation on the NIH VideoCasting site where Fitzpatrick speaks about his work.

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