2.6 Forebrain Subcortical Structures Control Your Motivations and Emotions

Thalamus Suppose you are served a platter of fajitas. You see the food and hear it sizzle. When you eat it, you feel it pass your lips and you taste it. The thalamus is critical in this process because it is the sensory gateway to the cortex (see Figure 2.16). It receives almost all incoming sensory information: sight, sound, touch, and taste. The thalamus also organizes this information and relays it to the cortex. But what about the smell of the fajitas? Smell has a direct route from the nerves in the nose to the cortex. So the smell of the fajitas would bypass your thalamus and be processed directly in your cortex. In addition, during sleep, the thalamus partially shuts out incoming sensations to help you stay asleep.

Hypothalamus The hypothalamus is the brain’s master regulatory structure (see Figure 2.16). In other words, it keeps the body “in balance”—not too hot or cold, hungry or full, sleepy or awake. Because of this role, the hypothalamus is indispensable to the body’s survival. Hypo means “below,” and the hypothalamus is located below the thalamus. The hypothalamus regulates body rhythms such as sleeping and waking, body temperature, and blood glucose (also known as blood sugar). It is also involved in basic motivated behaviors, including drinking, eating, aggression, and sex.

Hippocampus The hippocampus plays a critical role in the formation of new memories (see Figure 2.16). Its name comes from the Greek word for “seahorse” because of this structure’s seahorse-like shape. It is likely that the hippocampus forms new memories by creating new neural connections within the cerebral cortex for each new experience. New memories are not stored in the hippocampus itself; instead, permanent memories are stored in parts of the cortex (Takehara-Nishiuchi, 2020; Tanaka et al., 2018).

The hippocampus also helps you navigate in environments (Nadel et al., 2013). It may be particularly involved in how you remember the locations of places and objects. For example, it may help you recall how streets are laid out in a city or how furniture is positioned in a room. An interesting study to support this theory focused on London taxi drivers. The researchers (Maguire et al., 2003) found that one region of the hippocampus was much larger in London taxi drivers’ brains than in the brains of most other London drivers. London taxi drivers are well known for their knowledge of the city’s streets, so this research suggested it is possible that the hippocampus changes with experience to aid memory for locations. But correlation does not prove causation. To establish causation, the researchers later followed a group who trained for four years to become licensed London taxi drivers. They used brain imaging before and after training and compared brain changes to a control group who did not receive training. This study showed that the training was responsible for the growth in the hippocampus (Woollett & Maguire, 2011).

Amygdala The amygdala is located immediately in front of the hippocampus (see Figure 2.16). Its name comes from the Latin word for almond because of the structure’s almond-like shape.

The amygdala is important for processing the emotional significance of stimuli around you, especially for things that make you afraid (Fox & Shackman, 2019). As you walk through the woods and come across a snake, your amygdala helps you recognize that threat and makes you jump back to avoid being bitten. Do you find meeting new people threatening? People who are prone to anxiety show greater activation of the amygdala when viewing faces they have not seen before (Schwartz et al., 2003).

The amygdala also increases memory processing during times of emotional arousal. As a result, the amygdala serves a vital role in how you learn to associate things in the world (such as a snake) with emotional responses (such as fear). For example, a frightening experience can be seared into your memory for life (Kensinger & Ford, 2020). Even if your memory of the event is not completely accurate, in your mind the event can still be associated with great anxiety.