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[MUSIC] Of course, it would be very interesting to investigate the activity of the single neuron during the decision making process. This quite difficult task because neurons are quite small objects. So, the typical size of the neuron is between 10-50 micrometers. So here, you see on this graph, it's a very small object compared to the tip of the pencil. So, how to investigate the activity of this very small neuron. We can, of course, visualize the structure of this neuron using, for example, the electronic microscopy. But we also can put a small sensor, small electrode near this neuron, or inside of this neuron, and record the activity of the single neuron. So, as you remember, the neuron is a main computational element of our brain. So, done right, the accumulating information from other neurons. The cell body integrates this information and produces action potential, and action potential propagates the exon and sends the signal to other neurons, or to our muscles. So, we can record the activity of one neuron using single cell recording method. So we put a very small electrode inside of the neuron, or nearby, and we can record the single action potentials produced by the neuron. The more active the neuron is, the higher number, the higher frequency of the action potentials is produced by the neuron. So, overall, the neuron is a major computational element of the nervous system. So a neuron accumulates information. Neuron is activated by other neurons all by the sensory organs. And if this activation exceeds a certain threshold, the action potential is produced. And the action potential propagates the exon and activate by the release of the neuromediators, the muscles, or the next neuron. So, how can we study the neuron activity during the decision making process? We can implant an electrode to the brain of the animal and train the animal to perform certain tasks. Or for example, to pay attention to the screen. So I just give you a few examples of the reactions of different neurons to certain stimulus. So, the presentation of this stimulus is indicated by the black line in this graph. So you see that different neurons react very different, differently to the same object. Each line, vertical line here, represents one spike, one action potential. So, you clearly see that the first neuron produces a lot of spikes, a lot of action potential, during the presentation of the stimulus. The second neuron actually reacts to the offset of the stimulus, and the third neuron reacts to the onset and to the offset of the neuron. On the right side of this picture, we represent the same data slightly differently. So we make a histogram. We calculate the firing rate, the number of spikes per second. And we will use these graphs quite a lot during the next lecture. So, on these graphs, we clearly see that neurons are activated by the stimulus. And the first neuron is active during the presentation of the stimulus, the second neuron is activated by the offset of the stimulus. And the third neuron is activated most by the onset and offset of the stimulus. So during the course, you will see this kind of pictures. So here, monkey has to get food from the food box. He sees a representation of the activity of the neuron, and each dot here represents a spike. So, each line represents a trial. So what do we see here is that this neuron is particularly active when monkey touches the reward. So this neuron reacts to something that has a value. We can visualize this reaction of the neuron using a histogram.