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How Many Hemispheres Does The Brain Have

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Conflict Of Interest Statement

Why Do Our Brains Have Distinct Hemispheres?

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


Herculano-Houzel, S., and Lent, R. 2005. Isotropic fractionator: a simple, rapid method for the quantification of total cell and neuron numbers in the brain. J. Neurosci. 25:251821. doi:10.1523/JNEUROSCI.4526-04.2005

Azevedo, F. A., Carvalho, L. R., Grinberg, L. T., Farfel, J. M., Ferretti, R. E., Leite, R. E., et al. 2009. Equal numbers of neuronal and nonneuronal cells make the human brain an isometrically scaled-up primate brain. J. Comp. Neurol. 513:53241. doi:10.1002/cne.21974

Herculano-Houzel, S., Manger, P. R., and Kaas, J. H. 2014. Brain scaling in mammalian evolution as a consequence of concerted and mosaic changes in numbers of neurons and average neuronal cell size. Front. Neuroanat. 8:77. doi:10.3389/fnana.2014.00077

Herculano-Houzel, S., Avelino-de-Souza, K., Neves, K., Porfírio, J., Messeder, D., Mattos Feijó, L., et al. 2014. The elephant brain in numbers. Front. Neuroanat. 8:46. doi:10.3389/fnana.2014.00046

Brain Sulci Or Fissures

Below is a listing of several key sulci/fissures in the brain and the divisions they create.

  • Interhemispheric : This is a deep furrow located down the center of the brain that separates the left and right brain hemispheres. The corpus callosum, a wide ribbon of nerves, is located within this fissure.
  • Fissure of Sylvius : This deep grove separates the parietal and temporal lobes.
  • Central Sulcus : This sulcus separates the parietal and frontal lobes.
  • Collateral Sulcus: This furrow separates the fusiform gyrus and the hippocampal gyrus on the lower surface of the temporal lobes.
  • Parieto-occipital Sulcus: This deep crevice separates the parietal and occipital lobes.
  • Calcarine Sulcus: This groove is located in the occipital lobes and divides the visual cortex.

The Cell Structure Of The Brain

The brain is made up of two types of cells: neurons and glial cells, also known as neuroglia or glia. The neuron is responsible for sending and receiving nerve impulses or signals. Glial cells are non-neuronal cells that provide support and nutrition, maintain homeostasis, form myelin and facilitate signal transmission in the nervous system. In the human brain, glial cells outnumber neurons by about 50 to one. Glial cells are the most common cells found in primary brain tumors.

When a person is diagnosed with a brain tumor, a biopsy may be done, in which tissue is removed from the tumor for identification purposes by a pathologist. Pathologists identify the type of cells that are present in this brain tissue, and brain tumors are named based on this association. The type of brain tumor and cells involved impact patient prognosis and treatment.

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Injury In The Left Hemisphere Of The Brain

Since the left hemisphere of the brain controls the right side of the body, any injuries in it could lead to right-sided weakness. The following problems could arise:

  • Difficulty understanding both written and spoken words.
  • Difficulty expressing both written and spoken words.
  • The person finds it difficult to coordinate or program motor movements for speaking or medically called apraxia.
  • Slurred speech or change in the sound of the voice .
  • Difficulties with numbers.
  • Difficulty in dealing with complex problems.

Free Recall But Not Recognition Memory Is Impaired In Each Cerebral Hemisphere

How to Sync The 2 Hemispheres of Your Brain for Better ...

We have recently looked into information-processing capacities and sometimes have been able to compare postoperative performance with preoperative capacity. In these new tests, an interesting picture emerges: commissurotomy affects free recall mechanisms but recognition memory remains largely unchanged . Free recall requires a subject, with no cueing, to recall prior information such as a previously studied word list. Recognition tasks merely require a subject to judge whether a stimulus such as a printed word has been seen before on a list. Moreover, only posterior callosal-sectioned patients have a free recall deficit patients with their anterior callosum sectioned behave normally. Since sectioning the posterior callosum inevitably involves sectioning the hippocampal commissure, this structure may play a crucial role in memory deficit. It is as if the resources for encoding a stimulus that contributes to free recall are less available after disconnection involving the hippocampal commissure.

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Language And Speech Processes Of The Left And Right Hemispheres

A dichotomy that is useful when trying to understand the neural substrates of language is the distinction between how the brain enables grammar and how it enables a lexicon. The grammarâlexicon distinction is different from the more traditional syntaxâsemantic distinction commonly invoked to understand the differential effects of brain lesions on language.

In general terms, grammar refers to the rule-based system humans have for ordering words to facilitate communication. The lexicon is the mind’s dictionary in which words or groups of words are associated with certain meanings. The reason for using the grammarâlexicon distinction is that it takes into account the existence of units like idioms that can be learned by rote and form a single entry in the lexicon. While the lexicon cannot underlie most phrases and sentences because there is an endless number of unique sentences, such as the one I am currently writing, memory does play a role in the use of many short phrases . Thus, when uttered, such word strings do not reflect an interaction of syntax and semantic systems. They are, instead, an entry in the lexicon.

Implications For Understanding Some Neurological Syndromes

Clinical neurologists have described a variety of peculiar syndromes, such as anosognosia, that affect the perceptual and cognitive systems . Patients with anosognosia claim that the left half of their body is not theirs. They see their paralysed left hand and yet maintain that it has nothing to do with them. Although the region of brain damage associated with this syndrome is known, it is still difficult to understand why damage to the parietal lobe causes such bizarre behaviour in the patient. Other types of neurological damage can cause equally extraordinary symptoms. The concept of the interpreter, derived from split-brain research, may provide a way of understanding the more extraordinary results of cortical damage.

Consider what may happen as a result of a lesion in a person’s optic tract. If the lesion is in the nerve that carries information about vision to the visual cortex, the damaged nerve ceases to carry that information the patient complains that he is blind in the relevant part of his visual field. For example, such a patient might have a huge blind spot to the left of the centre of his visual field. He rightly complains.

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Brain Size And Gross Morphology

The human brain is a relatively small organ sitting within the skull and protected by membranes called the meninges, which include an external dense outer layer, called the dura mater, a thin inner layer, called the pia mater, and an intermediate layer, the arachnoid, constituted as a layer of fibers. The brain floats in a clear fluid, the cerebrospinal fluid , which has a protective role against trauma, as well as nourishing and draining functions.

FIGURE 1. Lobar parcellation of the external surface of a brain hemisphere. Red: frontal lobe, blue: temporal lobe, green: parietal lobe, yellow: occipital lobe. Lobar parcellation of the internal surface of the hemisphere. The cingulate gyrus, which spans the hemisphere’s entire internal boundary and which is part of the limbic lobe, is drawn in pink. The corpus callosum is the crescent-shaped structure nested just beneath the cingulate gyrus. The lobe known as the insula is not visible in this figure. The cerebellum, abutting the inferior surface of the brain, is in gray. External hemisphere major sulci . Internal hemisphere major sulci .

What Are The Cerebral Hemispheres And Why Are They Important

The two Cerebral Hemispheres

Its a long-standing myth that humans use only 10% of their brains. The fact is research shows that youre able to unlock your brains full potential by understanding how the cerebral hemispheres of the brain work.

The two hemispheres communicate with each other to control muscle function, speech, thought, emotions, reading, writing, and learning.

In this article, we will explore what a cerebral hemisphere is, where it is located, and what are specific functions of each part of the hemispheres.

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Some Right Hemispheres Can Develop A Writing System

A passive writing system can develop in the right hemisphere. One left-handed patient became agraphic following surgery. Five years after the surgery she remains unable to write at will, although she can produce her signature. When words are flashed to her dominant left hemisphere, she can say them out loud but she cannot write them . When words are flashed to her right hemisphere, she cannot say them but her left hand can usually write them . She cannot write the names of objects when pictures are lateralized, although she can match words and pictures accurately. This patient also shows semantic priming in her right hemisphere , indicating a semantic network in her right hemisphere. Nonetheless, without the executive skills of her dominant left hemisphere, her writing remains isolated and useless in the non-dominant hemisphere.

Gyri And Sulci Of The Brain

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The brain has a unique appearance that consists of many ridges and indentations. A brain ridge is known as a gyrus and an indentation or depression is a sulcus or fissure. Gyri and sulci give the brain its wrinkled appearance.

The cerebral cortex, or the outer layer of the cerebrum, consists of gyri that are typically surrounded by one or more sulci. The cerebral cortex is the most highly developed area of the brain and is responsible for higher brain functions such as thinking, planning, and decision making.

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Some Right Hemispheres Can Develop Speech

One of the hallmarks of most split-brain patients is that they speak out of the left hemisphere and not the right. This observation is consistent with the neurological literature and Amytal studies, in which the left hemisphere is the dominant hemisphere for language and speech .

There are now three and possibly four split-brain patients who can speak out of each hemisphere. While there is always an initially dominant hemisphere after brain bisection, some patients have developed the capacity to make one-word utterances from the disconnected right hemisphere . This rather startling development shows that two of the three major systems in human language can be managed by either hemisphere. Whereas patients P.S. and V.P. could speak in response to stimulation of the left visual field soon after the completion of surgery, patient J.W. did not develop this right-hemisphere capacity until â¥10 years after his surgery . This change so long after surgery opens up new questions regarding behavioural plasticity in the adult brain.

How Many Lobes Does The Brain Have

Brain Jack Image: Brain Hemispheres


Accordingly, what are the lobes of the brain?

The four lobes of the brain are the frontal, parietal, temporal, and occipital lobes . The frontal lobe is located in the forward part of the brain, extending back to a fissure known as the central sulcus. The frontal lobe is involved in reasoning, motor control, emotion, and language.

Additionally, how many Cerebellums are there in the brain? They are also easily the most numerous neurons in the brain: In humans, estimates of their total number average around 50 billion, which means that about 3/4 of the brain’s neurons are cerebellar granule cells. Their cell bodies are packed into a thick layer at the bottom of the cerebellar cortex.

Secondly, how many lobes does a human brain have?

Each side of your brain contains four lobes. The frontal lobe is important for cognitive functions and control of voluntary movement or activity. The parietal lobe processes information about temperature, taste, touch and movement, while the occipital lobe is primarily responsible for vision.

What is the largest part of the brain?


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Is There Only One Rule To Build Brains

Even though the parts are the same, this does not mean that brains of the same size are built of the same amounts of each kind of cell. It is also not true that a bigger brain is always made of more cells than a smaller brain.

We can think about this with an example. Imagine that you receive two brains of the same weight but belonging to different species. This is what we see in Figure 2: a rhesus monkey brain and a capybara brain . Both brains weigh about 80 g. You would probably say the brains have the same number of neuronsand so would many scientists. Until about 10 years ago, most researchers expected brains of the same size to have the same number of neurons. They thought that there was only one recipe in nature for building brains, and that all brains were made the same way. That also meant that the bigger the brain, the more neurons it would have.

  • Figure 2 Nature has different ways of adding neurons to primate and rodent brains as they change in size from one species to another.
  • This means that when a rodent brain gets larger, it does not gain many neurons. In contrast, when a primate brain gets bigger, its number of neurons grows more or less in proportion to how much larger the brain is.

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Anatomy Of The Human Brain

The largest part of the human brain is the cerebrum, which is divided into two hemispheres, according to the Mayfield Clinic. Each hemisphere consists of four lobes: the frontal, parietal, temporal and occipital. The rippled surface of the cerebrum is called the cortex. Underneath the cerebrum lies the brainstem, and behind that sits the cerebellum.

The frontal lobe is important for cognitive functions, such as thought and planning ahead, and for the control of voluntary movement. The temporal lobe generates memories and emotions. The parietal lobe integrates input from different senses and is important for spatial orientation and navigation. Visual processing takes place in the occipital lobe, near the back of the skull.

The brainstem connects to the spinal cord and consists of the medulla oblongata, pons and midbrain. The primary functions of the brainstem include relaying information between the brain and the body supplying most of the cranial nerves to the face and head and performing critical functions in controlling the heart, breathing and levels of consciousness .

The cerebellum lies beneath the cerebrum and has important functions in motor control. It plays a role in coordination and balance and may also have some cognitive functions.

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There Is Decoupling Of Spatial But Not Temporal Processes After Callosotomy

Franz and colleagues showed that commissurotomized patients could coordinate two conflicting spatial programmes, whereas a normal control was impaired . In effect, the spatial maps associated with a movement could be localized and isolated in each separated hemisphere. At the same time, while spatial information between the limbs remained separate, the temporal coordination of a bimanual movement remained largely intact.

In following up a partially sectioned patient, Eliassen and colleagues discovered that the integration of direction information for two-handed movements takes place exclusively across the posterior corpus callosum . They showed that the timing of a movement’s initiation is affected by anterior and posterior callosotomy. The ability of the two hands to move simultaneously was affected by the callosal surgery. Thus, the distribution of spatial and temporal signals to integrate bimanual movement is dissociable with regard to callosal topography. Posterior cortical areas, the parietal lobes, are the source of a spatial motor signal used during bimanual movements. Eliassen and colleagues went on to show that anterior and posterior fibres are not equipotential . Anterior callosotomy disrupts the simultaneity of self-initiated bimanual movements more than it does the production of bimanual movements in response to a visual stimulus.

What Are The Basics About The Lobes Of The Brain

Do People Really Have Right or Left Brain Personalities?

Anatomically, it is very easy to recognize the division that exists between the two hemispheres of the brain, because seen from above a remarkable space keeps them separated.

It is the interhemispheric fissure, which is something like a rectilinear crack that separates the upper and more superficial parts of the brain and defines where one cerebral hemisphere begins and where another ends.

However, beyond this obvious sign thanks to which we can get a very superficial idea about the anatomy of the brain, if what we want to examine is the structure of each of these elements, things get complicated.

Each hemisphere is covered by a layer called the cerebral cortex , and this cortex can be divided into different sections according to its different functions and locations.

This classification into differentiated areas within each of the cerebral hemispheres shows us the existence of several lobes of the brain. Lets see how they are.

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What Are The Specific Functions Of Each Cerebral Hemisphere

Each of the two hemispheres has its functions in what experts refer to as lateralization. The right cerebral hemisphere helps with vision independence, sense of touch, and object recognition. On the other hand, the left cerebral hemisphere assists in language, logical reasoning, and comprehension.

The hemispheres communicate through the wide flat bundle of neural fibers called corpus callosum.

At the first sight, its pretty obvious that each cerebral hemisphere hemispheres have its dominant functions.

Left hemispheres being responsible for speech, logical reasoning, and language processing and comprehension. And right responsible for spatial tasks identifying objects and spaces with any other senses apart from vision.

Thats probably why so many people believe they are left or right-brained. And even though each of the hemispheres has some dominant functions, both of them are directly involved in most of the bodily processes.

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