How the Brain Coordinates Movement in Animals

Animals are pretty skilled at using their bodies to get what they want, like food or water. They have to coordinate lots of different movements across their bodies to achieve their goals. For example, when rodents or monkeys want to eat something, they reach out with their arms, grab the food, and then bring it to their mouths. This all happens in a smooth sequence, with their senses helping them along the way.

Most of us know that behaviors like reaching and eating involve a lot more than just flailing our arms around. Decades ago, a smart guy named Lashley pointed out that movements are organized and happen in a particular order. But how the brain makes this all happen? That’s still a mystery.

#How Movements are Controlled

We know that the brain has special areas that help us with these actions. When you reach, grab, and lick, different parts of your brain are working hard. It seems like these movements don’t happen randomly; they follow a specific plan. The brain integrates signals from the body with feedback from the senses to fine-tune what you’re doing.

One area of the brain that helps manage movements is the cerebral CORTEX. This area is made up of different parts that deal with different tasks. Some parts help with planning movements, while others connect to lower parts of the brain that manage more basic actions. Research has shown that different parts of the cortex control different actions like reaching or licking. But how these brain circuits work together to coordinate complex behaviors is still something scientists are trying to figure out.

#The Brain and Movement Connections

In the cortex, there are different types of Neurons (or brain cells) with unique jobs. Some neurons help connect parts of the cortex together, while others send signals to deeper areas of the brain and spinal cord.

Among the neurons, two important groups stand out: one that sends information throughout the brain and another that directly talks to the thalamus, the brain’s relay center. The thalamus helps mix different types of information coming from the senses and the body’s state. It plays a crucial role in how the brain understands and responds to what’s happening.

#The Research and Its Findings

To dig deeper into how movements are coordinated, scientists combined tools like behavior analysis, imaging, and optogenetics (which is a way to control neurons with light) to study a specific behavior: the reach-and-withdraw-to-drink (RWD) task. In this task, mice are trained to use their sense of smell and touch to find and drink water from a spout placed at various locations.

They found that the secondary motor cortex (MOs-c) was a key player in helping the mice complete the RWD task. MOs-c coordinates the sequence of movements needed to reach for, withdraw, and drink from the spout. Two main types of neurons were identified as important: one that helps with reaching and another that supports the withdrawal and drinking phases.

#The Phases of Drinking

Let’s break down the RWD task into its parts:

1. Reaching: The mouse lifts its hand with its fingers curled and moves it toward the water spout.
2. Withdrawing: After grabbing the water, the mouse moves its hand back to its mouth.
3. Consuming: Finally, it opens its mouth and uses its tongue to lick up the water.

Interestingly, the timing of these movements varies each time. The researchers even looked at how long each part took and found that the mice were pretty quick on their feet, adjusting their movements depending on where the water spout was located.

#Understanding the Role of the Brain

Scientists then looked at different parts of the cortex to see how they contributed to the RWD task. Using a clever method called Calcium Imaging, they could see which parts of the brain were active during each phase of the task. They discovered that the MOs-c area was heavily involved.

When they inhibited this area, the mice struggled to complete the RWD task. This was a big deal because it showed that MOs-c was crucial for not just reaching but also for coordinating the movements of the mouth and hand.

#The Output Channels of the Brain

The researchers also found out that the MOs-c area uses different channels to communicate with the rest of the brain. One set of neurons helps with sending instructions to lower brain areas that control movement, while the other set influences the thalamus and helps adjust actions.

In particular, the corticothalamic neurons (CTTle4) had an interesting role. They kept firing at a steady rate throughout the different phases of the drinking task, showing that they helped maintain coordination between hand and mouth movements.

#How Different Brain Cells Work

To understand how the different types of neurons in MOs-c function, the researchers tagged specific neuron types and recorded their activities during the task. They noted that pyramidal tract neurons (PTFezf2) had different firing patterns compared to corticothalamic neurons. The PT neurons were more active during the reaching phase, while the CTT neurons ramped up during the withdrawal and drinking phases.

These findings suggested that while both kinds of neurons were important, they had their specialties. One was more about executing the reach, while the other supported the ongoing actions during withdrawal and drinking.

#The Importance of the Thalamus

The thalamus has a special job in this entire process. It receives input not just from the cortex but also from various other brain areas. This means it can mix different types of information about movement and perception, helping the cortex make better decisions about what to do next.

When the researchers interfered with thalamic activity during the task, they noticed that the mice had trouble completing the RWD sequence. This was a strong indication that the thalamus was vital for action progression and coordination during the task.

#The Communication Loop

The study revealed a fascinating communication loop between the MOs-c area and the thalamus. The MOs-c area sends signals to the thalamus, which receives sensory and motor information from various sources. This thalamic information then loops back to the cortex, making it possible for the brain to fine-tune actions.

The MOs-c sends specific inputs to the thalamus, which in turn influences their output to other cortical areas. This ongoing interaction allows for better coordination of movement and sensory integration, helping the mice carry out the RWD task smoothly.

#Conclusion

In summary, the study showed that the secondary motor cortex is essential for coordinating complex movements, like reaching and drinking. The interplay between different types of neurons, especially between MOs-c and the thalamus, helps animals execute skilled behaviors. The findings highlight how important communication within the brain is for our everyday actions, and they shed light on the underlying mechanisms that make these actions possible.

While we’ve only scratched the surface, it’s clear that understanding these pathways can offer insight into both normal movements and disorders that affect motor coordination. And who knows? Maybe one day, we’ll understand why our pets sometimes look at us funny when we try to train them. Until then, let’s raise a glass to the marvels of animal movement!