10 (Or So) Crucial Brain Structures
The brain consists of many distinct functional areas. Some of these functional areas are anatomically distinct; other functions are spread out over many areas and not localized. In the cases where different brain areas are responsible for particular functions, destruction of those areas tends to lead to a severe loss of that function.
The areas listed here are those that have a known crucial importance for a particular cognitive function, are the subject of considerable current research, and are specifically affected by significant brain diseases such as Alzheimer’s and Parkinson’s diseases.
When you look at a human brain, most of what you see is neocortex. This mammalian feature dwarfs the rest of the brain, which it totally covers and nearly encloses. The neocortex is at the top of the processing hierarchy for all the senses, as well as for control of behavior.
The thalamus, gateway to the neocortex
The thalamus is the gateway to the neocortex. In each cerebral hemisphere, the thalamus is very near the center of the brain, passing information to and from various areas of neocortex. It is like the hub of a wheel that is the concentrator and distributor of all forces.
The thalamus is particularly important in making a fast, efficient link between the frontal lobes and the parietal, occipital, and temporal lobes. The information shuttled between these areas relates to attention, awareness, and consciousness.
In the search for brain areas that appear to control lots of other brain areas, neuroscientists are frequently led to the pulvinar, a nucleus in the most posterior region of the thalamus. This nucleus, which has widespread connections with all of the neocortex, is involved in attention, particularly visual attention and eye movements. The pulvinar appears to integrate vision and goal pursuit so as to link appropriate visual stimuli to context-specific motor responses, while managing visual processing to ignore irrelevant visual stimuli.
The cerebellum is one of the oldest parts of the vertebrate brain. It is also one of the largest in terms of the number of neurons, with some estimates placing the number of neurons in the cerebellum at more than the entire rest of the brain, including the neocortex.
The function of the cerebellum is to modulate and coordinate motor behavior. The cerebellum is also responsible for learning and enabling rapid motor sequences.
The cerebellum is also involved in cognition in terms of thinking about yourself or other people or things moving. For example, when you play chess, you have to imagine how the pieces can legally move and which of opponent pieces they’ll interact with when they do so. The cerebellum is activated during this thinking.
Based on all this info, you might think that damaging the cerebellum would lead to profound dysfunction or even death. However, the main effect of damage to the cerebellum is to make people clumsy. There are, in fact, several well-documented cases of people born without a cerebellum that lead almost completely normal lives.
The hippocampus is part of the brain that makes memories. This structure receives inputs from the entire neocortex and projects back out to the same areas.
The storage in the hippocampus is temporary, however. The hippocampus can play back a sequence of events in context and activate the cortical areas that were activated by the event itself. This playback occurs typically during sleep, especially during REM sleep. The result of the playback is that the memories that were stored for a short term in the hippocampus cause long-term storage back in the neocortical areas that were activated during the original episode.
Wernicke’s and Broca’s areas
Wernicke’s and Broca’s areas are instrumental in language. Wernicke’s area, at the border between the superior temporal lobe and the parietal lobe, functions as a high order auditory association area.
The function of Wernicke’s area is to process speech. Wernicke’s area also has to help extract meaning from sentences according to grammar. In doing this, it interacts with other brain areas also, including Broca’s area in the frontal lobe.
The language functions of Wernicke’s area are carried out primarily on the left side of the brain of 95 percent of right-handers and a majority of left-handers. Damage to Wernicke’s area results in reduction in the ability to comprehend and produce meaningful speech. The area on the right side of the brain corresponding to Wernicke’s on the left processes tone of voice indicating irony, humor, and other aspects of prosody.
Broca’s area is located in the frontal lobe (approximately Brodmann area 40) just anterior to the areas of primary motor cortex responsible for controlling the tongue, lips, and other speech articulators. Damage to Broca’s area results in difficulty in producing speech. Severe damage to Broca’s area can also reduce some aspects of speech comprehension as well.
The fusiform face area
The fusiform face area (FFA) is a region of the medial temporal lobe that underlies your ability to recognize faces. It may also function in your ability to recognize purpose in some kinds of behavior.
The FFA is close to the end of the ventral visual pathway processing stream. Here are the cells that selectively respond to faces, hands, and other biologically significant stimuli.
There are several well-documented case studies of patients with damage to FFA. When damage includes the right FFA particularly, patients lose the ability to recognize faces, even their own, though they may be able to distinguish other similar looking objects like cars or animals.
The amygdala has extensive connections with low-level sensory systems through the thalamus and a portion of the prefrontal cortex called the ventromedial (or orbitofrontal) cortex. The amygdala also has connections directly from the hippocampus, which is just posterior to it.
The amygdala functions as a memory system for emotionally salient events. However, unlike the hippocampus, which works with the neocortex to reproduce a cortical representation of some event of which we can become conscious, the amygdala produces unconscious autonomic responses of fear, disgust, or apprehension to salient stimuli.
There have been well-documented cases of damage to the amygdala resulting in the person lacking concern for the suffering of others, including extreme cases in which those with amygdala damage inflict suffering without remorse or empathy.
The lateral prefrontal cortex
Working memory is the representation of what is salient about the current situation. The main brain area responsible for working memory is the lateral prefrontal cortex. This area of the neocortex receives inputs from the rest of the neocortex, the thalamus, and the hippocampus, and makes reciprocal connections back to many of these areas. Little is known about functional subdivisions within this large area of the prefrontal cortex, which is nonetheless essential for abstract thought.
The lateral prefrontal cortex is the seat of rationality and the part of the brain that most liberates people from purely instinctive behavior. By enabling the representations of things that are not actually in front of you at the present time, it permits planning and complex goal pursuit. The lateral prefrontal cortex is also essential for episodic memory, the memory for a particular event, in the context of the situation around that event, as opposed to memories of facts or general associations.
Damage to the lateral prefrontal cortex impairs the ability to act in a manner appropriate to current circumstances and to change goals or sub-goals in response to real world contingencies. Behavior becomes more stimulus-driven and stereotyped.
The substantia nigra (basal ganglia)
The basal ganglia are a complex, interconnected set of subcortical nuclei that control behavior at the level below the neocortex. The substantia nigra performs a crucial modulatory role in this system.
One reason that the basal ganglia have become relatively well known is Parkinson’s disease, which is caused by a degeneration of dopamine producing neurons in the substantia nigra.
The anterior cingulate cortex
The anterior cingulate cortex (ACC) is the anterior part of the cingulate gyrus, located just above the corpus callosum and below the neocortex. It is not neocortex but mesocortex, an earlier type of cortex that evolved as the top of the hierarchy of the limbic system.
The anterior cingulate is special because it seems to control neural processing throughout the neocortex, allocating this processing according to task demands. It is also implicated in subjective experience associated with consciousness, particularly consciousness of pain. The anterior cingulate is activated by pain and even the anticipation of pain. Electrical stimulation of the ACC can eliminate the perception of pain without removing the sensation of the stimulus that is painful.
The ACC is also activated when you struggle with a difficult task, particularly when you make errors. This activation is part of the ACC’s role in allocating neural processing across the neocortex according to task demands. In this function, it works with and is extensively connected to the lateral prefrontal cortex. In this regard, you can think of the lateral prefrontal cortex as holding the content of thought and the ACC as selecting that content.