What Part of the Brain Controls Smell?

This blog answers “What part of the brain controls smell?”. The blog will also highlight the functions of the cerebral cortex in detail, and some facts about the brain. The blog will answer some frequently asked questions about the brain in the end.

What Part of the Brain Controls Smell?

The sense of smell is controlled by the olfactory cortex. The olfactory cortex is a part of the cerebrum and is a portion of the cerebral cortex. It is a very small yet distinct region of the cortical structure. 

It is situated on the central surface of the forebrain. The olfactory consists of several areas within it, including the piriform lobe as well as the hippocampal formation. 

Olfactory Cortex:

The olfactory cortex is important for the processing as well as the perception of odour. It is a part of the limbic system. The Limbic system is another part of the brain that helps in processing emotions and behaviour. The thalamus is an egg-shaped part above the brainstem and helps filter sensory information from the spinal cord and it passes through the reticular formation. They also help in relaying signals to higher regions of the brain (Sherman & Guillery, 2006). 

The thalamus shuts off various incoming signals from the senses and allows us to rest. Hence, it plays a significant role in sleep.  The thalamus receives important signals from several higher brain regions and forwards them to the cerebellum and medulla. 

The amygdala is primarily responsible for the regulation of fear, aggression and perception. It consists of two almond-shaped clusters. It is connected to other bodily functions such as facial expression, and the sympathetic nervous system, which is important in regulating fear response. 

It is also responsible for the release of neurotransmitters which is related to processing aggression and fear, as well as processing smell (Best, 2009). 

Humans have a very strong and complex sense of smell. It is codependent on sensory organs, nerves, and the brain. Humans possess 4 million cells in our noses which are responsible for the smell. 

These 4 million cells are then divided into 400 different types of cells depending on their functions. Each of these smell cells carries a particular type of receptor on it, sometimes also referred to as a ‘lock’. 

The smell that floats through the air enters our nostrils and basically fits into the ‘lock’ which activates the cell, and so does our perception of smell begins. 

The olfactory system is one of the most primitive systems in the history of humans when it comes to sensory systems. This is because it has connections with older, subconscious parts of the brain such as the limbic system. 

Thus, this is the reason why smell is successful in activating intense feelings and memories that are associated with that particular odour. 

However, the messages received by the olfactory cortex are also sent to higher, conscious cortical areas for further processing. The messages enter the thalamus and then work their way up to the frontal cortex. 

Here, we identify the smell and other thought processes related to the odour that are processed. Thus, in this way, olfactory messages first enter the primitive brain where they trigger emotions and memories. They then travel to higher areas for deeper and rational processing. 

The Olfactory Nerve

The first cranial nerve (CN1) is the olfactory nerve that carries out functions of the sense of smell. Olfaction is considered to be the first sense we ever developed and thus is regarded as the oldest of the senses. It is carried out with the help of a unique visceral afferent nerve. In fact, CN1 is the only cranial nerve with the extraordinary feature of not having a cortical connection to the thalamus (Milardi et al., 2017).

Genetic Influence

The variation within the population for detecting and differentiating between odours is tremendous. Research has demonstrated that some people are unable to smell certain classes of odours, and they are likely to have a genetic difference from the rest of the general population. 

Anosmia is the inability to detect any kind of smell. It can be general or specific. About 5% of the world’s population is considered to be anosmic. On the other hand, hyperosmia is a condition where someone can have a heightened sense of smell, and this is also a genetically inherited trait. 

Interestingly, people who are born without an olfactory bulb can still have the sensation of smell. In a study, researchers found that a group of their normal control participants did not have an olfactory bulb, but they still scored normal scores on smell tests. They also found out that 0.6% of all women can smell as good with or without an olfactory bulb. This happens to be true for 4.3% of women who are left-handed. However, if a man does not have an olfactory bulb, they are unable to taste or smell anything they eat or witness.

Neurodegenerative Disease and Its Relationship with Smell

Research has increasingly been curious to know how the sense of smell is in individuals who are ageing or have neurodegenerative diseases. In diseases such as Parkinson’s disease and Alzheimer’s disease, olfactory dysfunction is in fact one of the earliest risk factors that appear. In fact, this symptom shows up way before motor symptoms and cognitive decline show up.

Thus, losing the sense of smell is considered to be the early signs of many neurodegenerative diseases as well as a marker of how the disease will progress. It is also a marker of when to start expecting a cognitive decline in these individuals. Thus, paying attention to olfactory function may prove to be helpful in improving one’s chances of a better outcome for neuroprotective and disease-modifying strategies.

Other Functions of the Cerebrum

The cerebrum is the largest part of the brain and is located in the front. It is responsible for movement, maintaining the temperature of the body, sense of touch, vision, and hearing. It is also involved in judgement, reasoning, problem-solving, emotions, and learning. 

The cerebral cortex is responsible for thinking and consciousness. Humans have a larger cerebral cortex compared to others. The cerebral cortex is the outer brake-like layer of the brain and allows individuals to use complex skills, live in social settings, use language as well as create tools (Gibson, 2002).

The Four Lobes of the Brain

Each hemisphere of the cerebral cortex is divided into two hemispheres and subdivided into four lobes, each of them is separated by folds known as fissures. 

The Frontal Lobe

The frontal lobe is in charge of problem-solving, judgment, decision-making, and motor functions (Stuss & Alexander, 2000).

The Parietal Lobes

The parietal lobes handle sensation, handwriting, as well as the position of the body.

The Temporal Lobes

The temporal lobes are responsible for memory and hearing.

The Occipital Lobes

The occipital lobes include the visual processing system of the brain.

Conclusion

This blog answered, “What part of the brain controls smell?”. The blog also highlighted the functions of the cerebral cortex in detail and some facts about the brain. The blog will answer some frequently asked questions about the brain in the end.

Frequently Asked Questions: What Part of the Brain Controls Smell?

What are the 3 basic units of the brain?

The three basic units of the brain are the forebrain, the midbrain, and the hindbrain. This is the usual way in which the brain is divided into.

What is not controlled by the cerebrum?

The function which is not controlled by the cerebrum is automatic control or autonomic functions. These functions are controlled by the spinal cord and the brainstem.

What are the three functional areas of the cerebellum?

The cerebrocerebellum, the spinocerebellum and the vestibulocerebellum  are the three functional areas of the cerebellum. Out of the three, the cerebrocerebellum is the largest section and is formed by the lateral hemispheres.

Which lobe controls the sense of smell and taste?

The parietal lobe is in control of the sensory information we receive from the five senses – vision, touch, smell, auditory information, and taste.

References

Marin C, Vilas D, Langdon C, Alobid I, López-Chacón M, Haehner A, Hummel T, Mullol J. Olfactory dysfunction in neurodegenerative diseases. Current allergy and asthma reports. 2018 Aug 1;18(8):42.Available from:https://pubmed.ncbi.nlm.nih.gov/29904888/ (accessed 27.12.2020)

Milardi D, Cacciola A, Calamuneri A, Ghilardi MF, Caminiti F, Cascio F, Andronaco V, Anastasi G, Mormina E, Arrigo A, Bruschetta D. The olfactory system revealed: non-invasive mapping by using constrained spherical deconvolution tractography in healthy humans. Frontiers in neuroanatomy. 2017 Apr 10;11:32.

Stuss, D. T., & Alexander, M. P. (2000). Executive functions and the frontal lobes: a conceptual view. Psychological research, 63(3), 289-298.