credit: A. Ajifo
Welcome to Brain Bits, where I highlight important or interesting recent news in the world of neuroscience. In store for today: recording the activity of an entire moving brain, sensing different types of touch, optogenetics trials in humans, and more!
Neuroscientists have long dreamed of recording the activity of every neuron in the brain at the same time: since everything the brain does is encoded by its pattern of activity, in theory this should give us all the information we need to figure out how it works. Techniques to observe neuronal activity using fluorescent sensors (instead of electrical probes) have paved the way for whole-brain recordings, particularly in small, transparent animals such as fish or worms. Two new studies in PNAS, which you can read here and here, now report the first examples of imaging whole-brain activity in a freely moving animal, the worm C. elegans. These experiments set the stage for exciting future studies examining the relationship between brain activity and naturalistic behavior.
Image of a neuron sensing gentle stroking, showing many small branches (from Bai et al., 2015)
Our skin is sensitive to many different kinds of touch, such as light pressure, heavy pressure, vibration, and stretching. Different types of neurons in our skin are specialized for detecting these different sensations. Over 50 years ago scientists identified neurons that sense gentle stroking of the skin, but no one ever figured out how they actually work. A new Cell paper from David Ginty’s lab uses sophisticated genetic tools to finally uncover how these touch neurons function. It turns out that these neurons have lots and lots of tiny branches distributed across the skin, and each branch is only weakly activated by touch. The key is that each neuron adds up all the activity it receives across all its branches, and it fires when many branches are activated in a short time. So gently stroking a wide area of skin will activate many branches and make the neuron fire, whereas poking one area won’t do anything. This study adds a big piece to understanding how our skin can sense so many different types of touch.
Neurons fire when they get activated by other neurons or by external stimuli, such as sights, sounds, or smells. Usually a neuron only fires for as long as the stimulus is present. However, some neurons keep firing long after the stimulus is gone, which is called persistent firing. Persistent firing is thought to explain how we can retain a short-term memory of a stimulus, like knowing that your coffee cup is on the table right next to you even though can’t see it at the moment. But scientists don’t really understand how persistent firing works: most theories involve feedback models where neurons activate each other in a loop. A recent study in PLoS Biology has now identified a new mechanism for how persistent firing can be generated at the level of a single neuron—no feedback loops required. Normally neurons fire when sodium and calcium ions move into the cell, and usually these ions are rapidly transported back out by various pumps. The new paper shows that when a neuron has an abnormally low level of a certain type of pump, the ions can’t leave the neuron quickly and so the neuron keeps firing. Read a summary of the paper here.
Stimulating a mouse brain using optogenetics- will humans be next?
An article in Scientific American describes how clinical trials using optogenetic therapies in human patients are set to begin soon. Optogenetics refers to using light to alter the firing of neurons. Since many brain disorders, from Parkinson’s disease to depression, have been linked to specific brain regions being too active or not active enough, using light to bring that activity back to normal might help treat these conditions. However, optogenetic treatments require not only delivering light into the nervous system, but also injecting a virus to genetically modify neurons so that they can respond to the light. Circuit Therapeutics, a company founded by optogenetics pioneer Karl Deisseroth and others, intends to start with clinical trials to treat chronic pain.
Nature’s last issue of 2015 included a fairly well-written and comprehensive overview of the factors still holding back women in science. The article focuses on issues beyond those relating to children, from sexism in letters of recommendation to hiring policies.
Speaking of underrepresented groups in science, even though it came out awhile ago I have to highly recommend this essay by Erich Jarvis, a professor at Duke, entitled “Surviving as an underrepresented minority scientist in a majority environment”. An amazing and inspiring life story.
Did you see any recent neuroscience news that you’d like to share? Leave a comment below!