![]() ![]() To further convince themselves that the neurons in the insula were responsible for the increased anxiety that they saw in mice with artificially elevated heart rate, they used a similar technique to shut down the insula. To confirm that the insula was a key player in producing anxiety during increased heart rate, they recorded from hundreds of insula neurons simultaneously using Neuropixels probes in live, awake mice and found that the insula neurons became active in real time when heart rate was elevated. This was interesting because the insula is known to connect areas of the brainstem with other parts of the brain that help produce emotions. They found that highly active neurons in several brain areas including the brainstem which is known to receive sensations from the internal organs of the body, but also an area called the insula. To visualize which areas of the brain were receiving interoceptive signals from the heart while it was artificially racing, the researchers then captured active neurons and performed whole brain clearing, in a technique similar to that discussed in a recent Neuroknow article. Compared to when their hearts were not stimulated, they spent more time sticking to the edges of the enclosure and seeking safety. So what did they find? Mice don’t like to be in open or exposed areas, and when the researchers increased the mouse’s heart rate in a risky context like a spacious, open cage, the mice exhibited significantly more signs of apprehension and anxiety. ![]() When they turned the red light off, the mouse’s heart rate always returned to normal.Įlevating heart rate changes mouse brains and behavior Using ChRmine and red LED light, the researchers could artificially boost a mouse’s heart rate up to 900 beats per minute, about 30% higher than the normal heart rate of 500-800 beats per minute! However they only did this for half a second every 1.5 seconds in order to mimic a particular heart arrythmia called tachycardia, and to make sure it did not adversely affect the mouse’s health. ![]() By controlling how fast the red light flashes, they can control the mouse’s heart rate. When the red light reaches the ion channels in the mouse’s heart, it causes the heart to contract. The flashlight isn’t showing red because of the blood in your hand, but because all of the wavelengths of light are blocked except for red which can pass through. The red light can reach the heart because its lower wavelength allows it to pass through skin, in the same way that your hand glows red when you hold up a flash light to it. The second part involves attaching a red LED light to a vest that the mouse wears, and shining it through the skin onto the heart. 5 The first part of this technique involves placing a special red light sensitive ion channel called ChRmine into the heart muscle cells. They used this novel method to ask whether increased heart rate alone can cause anxiety. In a recent paper, neuroscientists Brian Hsueh and Ritchie Chen from Stanford University introduced a solution to this problem with a new side-effect-free method of manipulating heart rate in mice. For instance, existing methods of influencing heart rate through electrical pacemakers or with heart medications can introduce unwanted side effects that may cause additional effects on emotions making it harder to study.Ī new method to make a mouse’s heart race 4 But studying how much internal bodily sensations contribute to an emotion can be tricky. ![]() 2,3 Interestingly, it is known that manipulating your facial muscles into expressions like a smile can activate the autonomic nervous system to mimic how the body feels during happiness, which can then lead to the genuine emotion of happiness. Much debate has taken place over just how much interoception influences emotion. This sensation of your internal bodily state is called interoception. Via the autonomic nervous system, the brain sends signals to internal organs like the heart, lungs, and gut but it also receives signals back. Many parts of the brain are needed to regulate your emotions, but emotions also activate a part of the nervous system that extends beyond the brain, called the autonomic nervous system, which is responsible for the famous ‘fight or flight’ (sympathetic) and ‘rest and digest’ (parasympathetic) responses. Emotional responses come from our brain and our body ![]()
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