In 1950, computer scientist Alan Turing devised a rather simple test for evaluating the intelligence of a computer. In the “Turing Test,” a human evaluator holds a conversation with two or more “people” in which one individual is secretly a computer. The computer tries to imitate a real person, and if the evaluator is fooled, then the computer has reached human intelligence. At the time, Turing estimated that computers capable of passing this test would be developed by the turn of the century. But as anyone who has talked to Cleverbot knows, we are still far from achieving this goal. Many computer programs, like Cleverbot and others, can believably fool an evaluator for a short bit of time through tricks and workarounds, but the illusion quickly falls apart. It’s difficult to simulate conversation because human intelligence and human communication are not algorithmic. When we talk to someone, our brains quickly integrate the basic language cues with contextual information like our memories and beliefs about the topic, the social and visual cues of the conversation, and our individual personalities. It’s a remarkably complex task that our 3-pound blobby brain accomplishes with comparatively little effort. So next time you put your foot in your mouth maybe cut your brain a little slack—turns out talking like a human is hard.
If we are to have any hope of building a robot that can pass the Turing test, we need to develop a much more robust understanding of human intelligence—from the coordinated behavior of neurons to the network of neural connections that make up the nervous system and brain. To understand the central nervous system a bit better, let’s follow the signals up. Nervous signals traveling towards or away from the brain must first pass through the spinal cord, the long stretch of thirty-one nerve pairs connecting the brain to the peripheral nerves. The spinal cord is broken up into four main sections—cervical, thoracic, lumbar, and sacral—that each govern the sensory and motor integration for different regions of the body. Most peripheral nervous signals pass through the spinal cord on the way to the brain, except for signals concerning the face or head that travel directly to the brain through cranial nerves. But for all other regions of the body, the spinal cord is the primary site of nervous signal integration. In addition to acting as a signal conduit, the spinal cord is also responsible for controlling the quick action of reflexes. When you touch a hot stove, your hand reflexively pulls away before your brain even has time to process that you’re in pain. Evolutionarily, this makes sense. Waiting the extra few seconds for the pain to register could mean irreparable damage. There are multiple different reflex arcs that the spinal cord manages—including the patellar reflex that doctors test when they tap your knee. Because they do not require any signals to or from the brain, these reflexes are completely subconscious and automatic (although your brain may become aware of them, like when visual cues cause you to consciously kick your doctor during a reflex test).
As we move up from the spinal cord, the functions of the brain become increasingly complex. The first region at the base of the skull is the brainstem, which is composed of the medulla oblongata, the pons, and the midbrain. The medulla oblongata (also called just medulla but that much less fun to say) is responsible for many autonomic processes like heart rate and respiration as well as some reflexes like swallowing, coughing, or vomiting. The pons is the main conduit for sensory signals into the brain. It’s also the primary point of connection for many of the cranial nerves that transmit sensory info from the face. A subregion of the pons called the reticular formation helps to filter out “background noise”—all the repetitive sensory stimuli that are considered irrelevant. The ability to filter sensory information like this is the reason you aren’t constantly distracted by the feeling of clothes on your body or the sound of a fan whirring. The reticular formation also filters pain signals, controlling how acutely you feel pain and what pain you focus on. Above the pons, the midbrain controls alertness, sleep, and homeostasis. A portion of the midbrain towards the back, known as the superior colliculus, is the primary integration point for visual input and the control of eye movement, and another region, the inferior colliculus, receives auditory input. Altogether, the brainstem is an important region for the conduction of sensory stimuli and the regulation of autonomic processes. As such, damage to the brainstem can easily result in coma or death. Damage to the pons is linked with a rare condition known as locked-in syndrome, where patients have full awareness and some eye movement but no ability to move their body or communicate.
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Behind the brainstem is the cerebellum—the region of the brain responsible for movement coordination and motor learning. While it works with the cerebrum to enact voluntary movement, the main role of the cerebellum is in regulating semi-conscious aspects of movement—maintaining balance and posture, regulating muscle tone, and timing and coordinating the movement of different body parts. Damage to the cerebellum doesn’t completely disrupt the ability to move, but it makes motor functions uncoordinated, unbalanced, or awkward. The cerebellum also plays a central role in motor learning through repetitive practice. Any action you perform routinely forms a muscle memory. The more you practice that action, the more coordinated and subconscious it becomes. Through muscle memory, the cerebellum is able to perform certain habitual actions without any conscious effort. Muscle memory is the reason why you might walk out the door one day and freak out about forgetting your wallet—only to find the wallet in your pocket. After several days of putting your wallet in your pocket as you leave, the action becomes habitual to the point that you may not even notice yourself doing it. And muscle memory also helps us learn and retain more complex actions, like playing a certain song on the piano. In fact, people with severe disruptions to their normal memory—like those with amnesia or dementia—are often still able to play complex songs that they learned prior to the memory loss. They may not even remember how they learned the song or anything else about it, but they still play it perfectly.
Just above the midbrain lies the diencephalon region of the brain, which contains the thalamus and the hypothalamus. The thalamus is the brain’s switchboard, relaying sensory and motor information to the proper areas of the larger cerebral cortex. It also regulates consciousness, awareness, and wakefulness. And it plays an important role in regulating sleep cycles—alterations in the connectivity of the thalamus have been linked to severe cases of insomnia. Just in front of the thalamus, the hypothalamus is responsible for regulating the body’s chemical signaling system—the endocrine system. The endocrine system is a much slower form of internal communication for the body that relies on the secretion of hormones into the bloodstream. These hormones can affect temperature regulation, appetite, fight-or-flight response, and reproductive cycles. The hypothalamus regulates the endocrine system by influencing the release of hormones from the pituitary gland in the brain.
Sitting on top of the thalamus, the cerebrum is the largest and most complex part of the human brain. The outer surface of the cerebrum is known as the cerebral cortex, and it is broken up into two mostly symmetrical hemispheres that each contain four lobes: the frontal lobe, the parietal lobe, the occipital lobe, and the temporal lobe. The frontal lobe is located at the very front of the brain, behind the eyes, and it is the primary center of conscious thought, planning, problem-solving, emotional regulation, and complex reasoning. The frontal lobe is also responsible for the nebulous quality we call personality. A famous example of how the frontal lobe impacts personality is the case of Phineas Gage. Gage was a railway worker in the 1800s who, in a tragic accident, had a metal rod propelled upward through his frontal lobe. He miraculously survived the accident and regained consciousness. But afterward, Gage’s friends and family noticed that his personality had completely shifted. He became irreverent, stubborn, and rude to the point that he lost his job at the railroad. Personality changes like this are also a symptom of frontotemporal dementia when neurons in the frontal and temporal lobes begin to break down.
Just behind the frontal lobe, the parietal lobe interprets sensory information related to sensations of touch (including temperature, pressure, and pain). It also maintains a sense of proprioception—the perception of where the body and limbs are in space. Behind the parietal lobe, at the very back of the skull, the occipital lobe processes and interprets visual input. Damage to occipital lobe can cause visual hallucinations. Finally, between the parietal lobe and the brain stem is the temporal lobe that processes auditory information and makes sense of visual cues like recognizable faces or scenes.
Deep within the brain is the hippocampus, the memory center of the brain involved in learning and long- and short-term memory storage. The hippocampus is also right next to the olfactory cortex, which processes the sense of smell. This is the main reason why certain smells become linked with particular memories.
In the frontal and temporal lobes of only the left hemisphere are Broca’s area and Wernicke’s area, regions of the brain devoted specifically to language. Broca’s area is in the left frontal lobe, and it is responsible for your ability to speak in complete, coherent sentences. Some people who suffer a stroke have damage to this area of the frontal lobe that results in Broca’s aphasia—a disorder characterized by the inability to use language coherently, despite thinking coherently. People with Broca’s aphasia can understand what others say to them and know how they want to respond, but their response comes out as gibberish. On the other hand, Wernicke’s area is in the left temporal lobe, and it is responsible for your ability to comprehend spoken language. People who suffer a stroke that damages this area have Wernicke’s aphasia—characterized by making frequent errors in what is otherwise fluent speech. People suffering from Wernicke’s aphasia often don’t recognize the errors in their speech unless it’s played back for them.
So, passing the Turing test would heavily rely on processes carried out by the Broca’s and Wernicke’s areas. It would also rely on complex thought and consistent personality carried out in the frontal lobe. Depending on the context of the conversation, there would be visual and auditory cues interpreted by the occipital and temporal lobes. And remembering the short- and long-term context of the conversation would rely on a functioning hippocampus. Coordinating all these sensory inputs would fall on the thalamus, and coordinating the motor outputs involved in speaking or typing would require the cerebellum. The architecture of the brain is interconnected and complex, so it’s no surprise that it has been so far impossible to replicate.
Science You Can Bring Home To Mom will be back in two weeks for a brand new series. For now, check out last month’s series on influential Black scientists of history. Comment on this post or email me at contact@anyonecanscience.com to let me know what you think about this week’s blog post and tell me what sorts of topics you want me to cover in the future. And subscribe below for weekly science posts sent straight to your email!
