Abstract
Your brain is an amazing control center that helps you see, hear, feel, think, and learn. Two important parts of your brain—the cerebral cortex and the thalamus—work together to help you understand and respond to the world around you. The thalamus acts like a message center, making sure information from your senses (such as sight, sound, and touch) gets to the right part of your brain. The thalamus also helps different areas of the brain talk to each other so you can think clearly and make decisions. It even helps you pay attention by focusing on the most important messages. This article explains how the thalamus works and why it is one of the brain’s busiest and most helpful team players.
How Does Your Brain Make Sense of the World?
The human brain is an incredible organ that helps you think, feel, and experience the world. Inside your brain, two important areas, the cerebral cortex and the thalamus (Figure 1), work together to help you understand the world around you [1]. The cerebral cortex is the outer layer of the brain responsible for thinking, learning, and problem-solving. The cerebral cortex could not do any of these tasks without its essential partner, the thalamus.
- Figure 1 - The cerebral cortex and thalamus.
- Side view of the brain showing regions of the cerebral cortex used for vision, hearing, touch, taste, and smell. The thalamus is located in the center of the brain and is also shown enlarged at the right. The thalamus also has different regions for processing each of the senses and these regions have connections with their associated cortical areas. Thalamus abbreviations: LGN, lateral geniculate nucleus; VPN, ventral posterior nucleus; MGN, medial geniculate nucleus; VPM, ventral posterior medial nucleus; MD, mediodorsal nucleus. This figure was made with the assistance of generative AI.
The thalamus is located in the center of the brain, buried deep underneath the cerebral cortex, and it has two important jobs. The first is to provide the cerebral cortex with sensory messages about the outside world. For example, if you are examining a beautiful flower in a garden, the thalamus will message the cerebral cortex about its color, shape, smell, and how it feels when you touch a petal. The second job of the thalamus is to help the many different areas of the cerebral cortex communicate with each other [1]. You can think of the thalamus as a sort of traffic cop that keeps traffic moving in busy intersections so that cars (or, in this case, the messages) reach their correct destinations in the cerebral cortex. Importantly, the thalamus may also help you pay attention to the most important messages, particularly when there are distractions, making sure the cerebral cortex receives those messages loud and clear.
Job #1: The Messenger of the Senses
The thalamus is about the size of a walnut and is located deep inside your brain. One of the thalamus’s most important jobs is to help you make sense of your senses. Humans have five major senses: sight, hearing, taste, touch, and smell (See this young minds article), and there are separate communication lines between the thalamus and cerebral cortex for each sense (Figure 1). When you see a rainbow, hear your friend’s laughter, or feel the soft fur of a pet, your thalamus is working hard to make sure your brain understands these experiences. Let us explore the sensations of sight, hearing, and touch and consider the role the thalamus plays in allowing you to experience those sensations.
Sightseeing With the Thalamus
Your eyes capture all the cool things around you (For more info check out this young minds article), and the thalamus makes sure that those visual messages are sent to the right part of your brain so you can recognize them. The eyes do not send messages directly to the cerebral cortex; instead, messages from the eye make a mandatory stop in the visual part of the thalamus where a group of specialized cells—the thalamic relay cells—transmit those messages to the region of the cerebral cortex called the visual cortex. The thalamic relay cells that transmit visual messages to the cerebral cortex are found specifically in a region of the thalamus called the lateral geniculate nucleus (LGN). Importantly, these LGN cells act as a gate, being wide open to let messages pass easily when you are alert and less open to reduce the flow of messages when you are drowsy or asleep.
Symphony of Sound
When you listen to your favorite song or the sound of raindrops, the thalamus helps your brain understand those sounds. It directs the information so you can recognize music, voices, and all the sounds that make your world musical and interesting. Sounds are first detected by specialized cells in your ears that transform the sound energy into electrical messages that make their way to another specialized region of the thalamus called the medial geniculate nucleus (MGN) (Find out more in this young minds article). Just like cells in the LGN for sight, cells in the MGN have very specific communication lines, but in this case, those lines project directly to the region of the cerebral cortex called the auditory cortex. Also, just like LGN cells, cells in the MGN also act as a gate to increase or decrease the communication of messages depending on how alert or sleepy you are.
Feeling Touch
Whether you are hugging a friend, holding a soft toy, or feeling the sand between your toes when walking on the beach, your thalamus makes sure your brain understands these sensations. Sensations begin with the activation of touch and pressure sensors in your skin that send electrical messages into your spinal cord and brain, eventually making their way to the thalamus (Check out this young minds article). A specialized region of the thalamus, the ventral posterior nucleus (VPN), relays those signals to the touch region of the cerebral cortex, called the somatosensory cortex, and, just like we discussed for vision and hearing, the communication of these messages is affected by how alert or drowsy you are.
Taken together, it is pretty cool how the different senses have specific communication lines but share similar strategies in how they relay their signals to the cerebral cortex.
Job #2: Teamwork Makes the Dream Work
You now know that there are multiple areas in the cerebral cortex for each of your senses and multiple areas for all of the other things the cerebral cortex is involved with, including emotions, the ability to make decisions, and the ability to speak and understand language [2]. These areas must send messages back and forth in order for us to think, understand, and generate appropriate behaviors. A different region of the thalamus, called the higher-order thalamus, plays an essential role in this function (Figure 2) [1].
- Figure 2 - How the higher-order thalamus helps brain areas communicate.
- (A) The brain can be viewed in three different planes: coronal, sagittal, and horizontal. These views allow scientists to examine structures deep inside the brain, including the thalamus. (B) A coronal view showing the cerebral cortex on the outside of the brain and the higher-order thalamus deep inside it. The arrows show pathways along which messages can travel in both directions between the higher-order thalamus and different areas of the cerebral cortex. These pathways help cortical areas communicate with one another. This figure was created with assistance from generative AI.
While the cortical areas can communicate directly with each other, they also send their messages to the higher-order thalamus, which makes sure those messages are relayed to the appropriate target areas within the cerebral cortex [1, 3]. This is not a straightforward task because every area within the cerebral cortex communicates with the thalamus, and the thalamus communicates with every area within the cerebral cortex. Fortunately, the thalamus has numerous specialized areas, each with specific communication lines to and from each of the separate cortical areas.
You might wonder why people have this alternative pathway through the thalamus when direct communication lines are present between cortical areas. Scientists are currently working hard to discover the answer to this important question. One of the most promising answers is that the higher-order thalamus can adjust which areas of the cerebral cortex are involved by changing the effectiveness of communication, to ensure the correct messages are being sent to the correct group of cortical players [4].
One strategy the brain uses to increase the effectiveness of communication is to align the timing of the messages being sent to a specific cortical area or group of cortical areas so that they can reinforce each other, much like how Viking oarsman synchronized the timing of their strokes to more efficiently move their ship forward. As the saying goes, “teamwork makes the dream work”! Additionally, recent research indicates that you can further improve the communication of messages between the higher-order thalamus and the cerebral cortex by the way you pay attention [4]. That is right, your brain has the ability to control how you use it… now that is something to think about!
Putting it All Together
In conclusion, the thalamus is a critical part of the brain, ensuring that you sense the world around you and correctly move messages between different cortical areas—allowing you to think, imagine, make decisions, and generate behaviors. It works tirelessly, helping your brain make sense of the amazing experiences life has to offer. So, the next time you enjoy a beautiful rainbow, hear a favorite song, or feel a warm hug, remember to thank your incredible thalamus for making it all possible! Now that you are an expert on the thalamus and cerebral cortex, take a look at the diversity of brain morphologies across the animal kingdom (Figure 3). Even though they have different cortical folding patterns and different looking thalamic nuclei, they all share the same partnership between the thalamus and cerebral cortex.
- Figure 3 - Photographs of slices of brain (coronal plane slices) from nine different animals.
- While each of these brains looks different, they share several common features. Importantly, across all of the brains, one can identify the cerebral cortex, which is the outer shell of the brain, and the thalamus, which is in the middle of the brain. These brains were stained with a bluish/purple dye that allows scientists to distinguish different structures in the brain.
Glossary
Cerebral Cortex: ↑ The outer layer of the brain that helps you think, solve problems, move your body, and feel emotions.
Thalamus: ↑ A small part deep inside your brain that acts like a message center. It helps your senses talk to your brain and helps different parts of your brain talk to each other.
Thalamic Relay Cells: ↑ Special cells in the thalamus that pass messages from your senses to the correct part of the cerebral cortex.
Visual Cortex: ↑ The part of the brain that helps you see. It is where messages from your eyes go so you can recognize faces, colors, shapes, and movement.
Lateral Geniculate Nucleus (LGN): ↑ A part of the thalamus that helps you see. It takes messages from your eyes and sends them to the visual part of your brain.
Medial Geniculate Nucleus (MGN): ↑ A part of the thalamus that helps you hear. It takes messages from your ears and sends them to the hearing part of your brain.
Ventral Posterior Nucleus (VPN): ↑ A part of the thalamus that helps you feel touch. It sends touch messages from your skin to the sensory part of your brain.
Higher-order Thalamus: ↑ Special parts of the thalamus that help different areas of the cerebral cortex send messages to each other.
Conflict of Interest
The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Acknowledgments
The author’s research programs are supported by the National Eye Institute: R01EY012576 (WMU), R01EY036242 (WMU), P30EY012576 (WMU), and R01EY017699 (SK), and the National Institute of Mental Health: R01MH137624 (SK), R01MH064043 (SK), P50MH109429 (SK), and P50MH132642 (SK and WMU).
AI Tool Statement
The author(s) declared that Generative AI was used in the creation of this manuscript. Generative AI was used for figure (cartoon images) generation and advice on age-appropriate vocabulary and phrasing.
Any alternative text (alt text) provided alongside figures in this article has been generated by Frontiers with the support of artificial intelligence and reasonable efforts have been made to ensure accuracy, including review by the authors wherever possible. If you identify any issues, please contact us.
References
[1] ↑ Usrey, W. M., and Sherman, S. M. 2022 Exploring Thalamocortical Interactions: Circuitry for Sensation, Action, and Cognition. Oxford: Oxford University Press.
[2] ↑ Halassa, M. M., ed. 2022. The Thalamus. Cambridge, MA: Cambridge University Press.
[3] ↑ Sherman, S. M., and Guillery, R. W. 2011. Distinct functions for direct and transthalamic corticocortical connections. J. Neurophysiol. 106:1068–77. doi: 10.1152/jn.00429.2011
[4] ↑ Kastner, S., and Usrey, W. 2023 “Attention and thalamocortical interactionsthalamocortical interactions”, in The Cerebral Cortex and Thalamus, ed W. M. Usrey, and S. M. Sherman. Oxford: Oxford University Press.