The famous American poet Emily Dickinson once said: “The brain is wider than the sky.” Her statement captures the boundlessness of the human brain, given that the brain is an intricate maze of billions of neurons. The orchestrated symphony of these neurons helps us perform simple to complex tasks daily.
The brain is primarily governed by two major parts—the cerebrum and cerebellum. Each part has designated functions; and simultaneously, a crosstalk between them for overall body control.
The cerebrum
The cerebrum is the most significant part of the brain, as almost 80 per cent of the tasks are coordinated and performed by it. It is located on top of the head and is fully covered by the skull. Dr Rashmi Devaraj, a paediatric neurologist at the National Institute of Mental Health and Neurosciences (NIMHANS), says, “Mainly, it [cerebrum] is associated with memory, language, communication and regulates the voluntary component of movement. In all, the cerebrum regulates sensory components like smell, vision, hearing, and touch.” Â Neurons are required to handle such great volumes of work, which are accommodated in grooves and ridges of the cerebrum. The folded structure, commonly known as they grey matter of the brain, Â houses the millions of neurons.
Divided but united
The cerebrum is visibly divided into two regions – the right and left hemispheres— by the great longitudinal fissure. A bundle of nerve fibres called the corpus callosum connects the hemispheres. “The hemispheres are connected to function synchronously,” says Dr Devaraj.
The left brain predominantly controls analytical and logical reasoning, problem-solving, judgement, and thinking. The right brain is involved in creativity, art, emotions, and intuition.
Each hemisphere of the cerebrum controls certain functions while coordinating with other regions. Dr Devaraj says that localisation and naturalisation of the brain parts are essential for working rhythmically. In addition, each hemisphere controls the opposite side’s body actions. For example, the left hemisphere actions the right-side body parts and vice versa.
Why the preferential hand?
While most of us are right-handed, some show left-handed dexterity and rarely is one ambidextrous (like the character portrayed by Boman Irani in the movie Three Idiots). Handedness or the preferential hand is the tendency to use one hand (either left or right) comfortably for skilled tasks such as writing or working. Hand preference originates from the body’s right-left asymmetry – a developmental process that differentiates the right and left sides of the body. As for the preferential hand, studies show that the more we use one hand, the stronger the neural pathways of that region. However, the synchronised division of work does not prove one-side dominance of the brain, says Dr Devaraj.
The five lobes of the cerebrum
The cerebrum controls conscious actions with the help of five lobes.
- Frontal lobe: It is in the front part of the head and helps in controlling attention, behaviour, decision making, speech, voluntary movement, and executive functions.
- Parietal lobe: It is located behind the frontal lobe. The parietal lobe helps in sensing touch and pain signals, gauges the distance and size of objects, and processes sound and the ability to use numbers.
- Temporal lobe: Present at the side of the brain, the temporal lobe helps in language processing, memory formation and speaking ability.
- Occipital lobe: It is at the back of the head, helping in visual processing, interpreting the depth and distance of an object, colour, and identification of objects.
- Insular lobe: Nestled beneath the frontal, parietal and occipital lobe, the insular lobe is responsible for taste perception, processing emotions and empathy.
Despite the division of lobes with dedicated functions, the cerebrum works as a single unit. “The five lobes coordinate through several neural networks and nerve tracts that connect each other and function as one,” says Dr Krishnan P R, senior consultant – Neurology, Fortis Hospital, Bengaluru.
Here is an example of how it happens. When we see a snack, the visual sensors in the eyes stimulate. The occipital lobe picks up these cues and acts on them. However, the decision to eat the snack is governed by the frontal lobe, which directs the limbs to move. Getting up and moving towards the snack requires the parietal lobe to gauge the distance and record the touch sense. As we savour the food, taste buds kick in, which triggers the insular lobe. The temporal lobe stores the entire process in memory that can be recalled when required. Similarly, each simple or complex task happens through the smooth coordination of the lobes.
What happens if the cerebrum is damaged?
Although the thick, bony skull protects the cerebrum, it is prone to damage. The cerebrum suffers physical damage due to falls and blows to the head. In such situations, the frontal lobe is affected the most, resulting in speech and cognition impairment and paralysis.
Dr Krishnan says the cerebrum is the most affected part of the brain during strokes and vascular diseases. He says a stroke on any side of the brain can cause paralysis on one side of the body or both sides, depending on the effect of the damage.
Metabolic disorders like diabetes can affect the brain and its function only when the blood supply is impaired, adds Dr Krishnan.
Psychiatric conditions like attention-deficit/ hyperactivity disorder (ADHD), depression and anxiety are functional disorders of any of the lobes, he says. No structural anomalies are seen in such conditions.
Just as tiny droplets make a mighty ocean, several neurons work together to make the cerebrum the master of all conscious actions, behaviour and personality that stands out uniquely.
