Lobes of the brain

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The diagram below shows the main physical brain structures.

brainlobes1

Limbic lobe

Limbic lobe – refer separate page for discussion and a description of the internal structures of the limbic lobe.  It is sometimes called the emotional brain, but really it only displays a few basic emotions.  We share this part of the brain with all other animals.  We differ from animals in that we have a more highly developed cerebral cortex.  The limbic lobe is connected to the brain stem and is within the outer lobes of the cerebral cortex that are visible in the diagram above, so the limbic lobe isn’t visible in the picture above.

Lobes of the cerebral cortex

The general flow of sensory information into the brain is through the brain stem and limbic lobe, and then into the cerebral cortex from the back starting at the occipital lobe, through the parietal and temporal lobes, and finally to the frontal lobe.

brain-flow

It is the pre-frontal cortex that we make decisions, and when we decide to take action this is initiated through the motor cortex.  Seems all very simple when viewed at this level.

Lets now look at each of the cerebral cortex lobes in a bit more detail.

Occipital lobe

Visual information from the eyes travels via cranial nerve II through the midbrain and Thalamus to the visual cortex V1 area in the Occipital lobe.  There is a small buffer of iconic memory in this lobe, which holds about 1 seconds worth of visual sensory data in “full resolution”.  The information is passed to the secondary visual cortex areas for further processing and interpretation.  Stereoscopic processing also takes place.

For additional information on visual processing, see here.  The sensory information is then passed via the Temporal lobe to the Frontal lobe.

Recent tests have shown that it is possible for humans to recognise an image flashed up for just 13 ms, but generally we need to see an image for at least a few hundred milliseconds to register and react to it.  If it flashes past too briefly it is discarded from the visual cortex.

The flashing of images for advertising purposes – subliminal advertising – is banned as it was discovered that recognition was actually taking place subconsciously and influencing our purchase choices.

Strobe flashing of lighting can trigger epileptic seizures that start in the Occipetal cortex and spread to other areas of the brain.

Parietal lobe

This is used for sensory processing (pain, touch, vibration, taste) and includes the sense of proprioception.

The Parietal lobe receives pain, vibration, temperature and pressure sensory information from all parts of the body, and builds a spatial map of the body location for navigation purposes (proprioception).

The taste perception area (gustatory cortex) also appears to be in the parietal lobe.

The language processing in this lobe is used to derive deriving meaning from numbers and mathematical symbols.

TPJ.png
(John A Beal)

Of particular spiritual interest is the function of the Temporoparietal Junction  or TPJ.  It has been found that damage or artificial stimulation of this area can cause people to have Out of Body Experiences (OOBE’s) similar to those reported during medical emergencies or during meditation.  It also seems that during long periods of intense meditation the circuitry in the parietal lobe can get confused, resulting in reported experiences of the body growing larger or smaller, or levitating.  This is a “brain error malfunction” rather than a spiritual experience or transcendence of the body, but is an area worthy of further research.

The TPJ plays a part in recognising social awkward situations, and does not function as expected in people with autism.

Temporal lobe

The Temporal Lobe is involved in processing sensory information (including sound), memory and language.  It attempts to derive sense and meaning from sensory information that has been received.

Although the auditory cortex resides in this area, its main function seems to be in deriving meaning from sensory input, especially sight and hearing.  The Fusiform Area (FFA) carries out facial recognition, and Wernicke’s area translates the words we see and hear.  Once we learn how to do this these functions work automatically for us (subconsciously).

Frontal lobe

This is the higher, conscious brain, where the Central Executive Network is located.  Functions such as decision making, planning, focus of attention, inhibition of socially unacceptable responses.  Once a decision is made to take action, voluntary movement is initiated from the motor cortex in the frontal lobe.

This is our top level executive decision-making centre, responsible for most of our conscious thinking.  Once sensory information has been received and processed by the other brain centres, the information is passed up to the frontal lobe and especially the DLPFC (dorso-lateral prefrontal cortex).  This is where working memory resides.  Data is fetched from our long-term memory if required, and decisions are made.  Actions are issued as instructions to the motor cortex and/or Broca’s area if talking is required.

This area has direct control over the eye focusing muscles (FEF) to quickly direct attention.  The IFJ area has also been found to be area we use when we want to focus our attention on something.

The OFC (orbifrontal cortex) or vmPFC (ventro-medial prefrontal cortex) gets involved in decision making and moral choices – where inhibitory behaviour is required.  It is this area that has the “off” switch for amygdala.  Sensory information may have fired up the amygdala into a state of anger, but the thinking process in the DLPFC and OFC, recalling past memories and experiences and considering possible outcomes of actions, is able to contain any emotional outbursts and suppress the instinctive emotions.  Spiritually developed people have control over their emotions.  How well we can maintain control in all situations depends a lot on how well we are able to use these higher brain areas.  We have the circuitry, we just need to learn how to use it properly.  The qualities and benefits that come from us properly using these areas of the Frontal lobe will be examined further in the Spiritual section.

The Frontal lobe depends a lot on the neurotransmitter Dopamine.  The presence of Dopamine receptors determines what motivates us and places our interest in certain things and not others.  This is both a good thing and a bad thing.  There will be more discussion on this and the reward network later.  The degenerative Alzheimer’s disease resulting in cognitive decline and dementia is linked to the decline of the dopamine system in these brain areas (it is not yet known why this happens).

Insular Cortex

Not shown and not visible is the Insular Cortex, as it is folded up behind the temporal lobe.  It was once classified as part of the Limbic lobe, but is now usually designated as a separate brain lobe, and is associated with self-awareness.  It is probably where our ego or personality lies.

It is widely interconnected with the other lobes, and is believed to be centre of body awareness and consciousness of the self.  “Sense of body ownership”, and emotional awareness.

Quoting directly from Wikipedia:  “the anterior insular cortex is believed to be responsible for emotional feelings, including maternal and romantic love, anger, fear, sadness, happiness, sexual arousal, disgust, aversion, unfairness, inequity, indignation, uncertainty, disbelief, social exclusion, trust, empathy, sculptural beauty, a ‘state of union with God’, and hallucinogenic state.

There is still some uncertainty of the exact brain location of the “ego”, but regions such as the Insular cortex, Anterior Cingulate and the Default Mode Network (DMN – to be discussed later) are key areas of interest.  Recent MRI imagery work with subjects taking LSD and/or DMT which seems to simulate the spiritual experience of losing ego identity all points to a reduction of activity in the Anterior Insular and general wider connectivity between the higher brain regions.  For those seeking spiritual enlightenment and a reduction in the power of the ego, the Insular cortex appears to be one of the brain regions where activity needs to be reduced.

Other brain structures

Briefly covering the few remaining areas from the brain diagram above:

Medulla oblongata – part of the reptilian brain.  It is part of the deep, unconscious brain.  It never sleeps.  It keeps our heart beating, blood flowing, and regular breathing.  Some spiritual masters such as Paramahansa Yogananda considered the medulla to be the gateway to superconsciousness.

Pons – nerve connectivity of sensory signals from the brain stem to the Thalamus in the limbic brain.  Most of external sensory nerve pathways go through here, and the source of many neurotransmitters are in the pons and mid-brain.

Cerebellum – part of the old reptilian brain; used for motor control.  Unlike most other structures in the brain which have a left and right hemisphere, the cerebellum is a single structure.

Postcentral and precentral gyrus, and central sulcus –  the postcentral gyrus is associated with touch, and the precentral gyrus with motor control of the hands and feet.