The Lobes

Dr. C. George Boeree

The Frontal Lobe

Starting from the central sulcus and working forward, we first have the motor cortex, which sends its signals down to the body to control the skeletal muscles.

Just in front of the motor cortex there is the premotor cortex, which is where we compose and rehearse movements before we engage in them.  Broca's area for speech production is part of the premotor cortex.

And then we have the prefrontal cortex, where some of the most interesting things occur.  Some say that will power, our sense of reality, and our sense of our own personality reside there.

A few areas of the prefrontal cortex are at least partially understood.  The dorsolateral area (high and to the sides) appears to allow us to hold ideas in awareness, focus on them, and even manipulate them.

The ventromedial area (low and close to the midline) seems to be involved in emotional experience and provides us with the feeling that things make sense and have meaning.  Low levels of activity here are associated with depression:  Nothing makes any sense.  High levels, on the other hand, are associated with mania:  Every little thing is full of importance!

The orbital area of the prefrontal cortex (just above the eyeballs) tells us when something is wrong and requires serious attention.  It also has the ability to inhibit behaviors that are inappropriate, such as those that are harmful to us or are socially unacceptable.  This includes the ability to counteract the signals for aggression from the amygdala in the limbic system.  It is believed that many violent criminals have had damage to this area of the brain.

In the most frontal part of the prefrontal lobe is an area devoted to interpreting people's intentions and motives.  Autistic people seem to have some sort of defect in this location.

The Temporal Lobe

This lobe sits at the two sides of the head, under the temples.  The upper part of the temporal lobe, along the Sylvian fissure that separates it from the frontal lobe, is the primary auditory cortex, which receives input from cochlea.  The areas around it are devoted to interpreting sounds, and one of these in particular (Wernicke's area, toward the boundary with the parietal lobe in the left hemisphere) is known to be devoted to the understanding of language.

Another area is called the fusiform gyrus, which sits low in the temporal lobe near the occipital lobe.  In the left hemisphere, it is responsible for word and number recognition.  In the right hemisphere, it is responsible for the crucial human ability to recognize faces.  Problems here leave one with a disorder called prosopagnosia ("face blindness"), which makes social life very difficult.

There are medial (inner) areas of the temporal lobes that are closely connected to the hippocampus and appear to be devoted to memory for life events (episodic memory).

One very odd function of the temporal lobe is what some have called the God spot.  Stimulation here gives people intense feelings of joy and the sense of being close to some greater power or being "one with the universe."  Some epileptic patients get these intense feelings just before seizures, and it is believed that some famous saints and other religious figures may have likewise suffered (if you can call it that!) from such disorders.

The Parietal Lobe

The furthest forward area of the parietal lobe, along the central gyrus nearest the frontal lobe, is the somatosensory area, which collects signals coming up from the body.  Just behind that is the somatosensory association area, which further analyzes these bodily sensations.  Specific areas specialize in locating and orienting us in three-dimensional space, and focusing on things in the outside world.

The Occipital Lobe

The occipital lobe is the smallest of the lobes and sits at the very back of the head.  It has no clear borders and is differentiated primarily by function, i.e. vision.  The various parts of the occipital lobe are labeled with a V (for visual) followed by a number.

The primary visual cortex at the very back of the occipital lobe is labeled V1, and receives input from the optic tract.  It has a clear map of visual information that corresponds to the areas of the retina.  The center of vision is greatly magnified.  The individual neurons of V1 are extremely sensitive to very particular changes in input from the eyes.

If there is a lesion somewhere in V1, there will be a "hole" in your vision called a scotoma.  Oddly, some of the information from that "hole" seems to still be available, so that some people with scotomas can still react to stimuli there even though they don't consciously perceive them!  This is called blindsight.

V2 surrounds V1 and has many reciprocal connections with it.  Much of its functioning is a repeat of V1's, but it detects more complex features, such as contours and the distinction between figure and ground.

V3, just above V2, gets inputs from both V1 and V2.  It appears to specialize in depth, distance, and global motion.

V4 lies under V2.  V4 is affected by attentional processes, and specializes in somewhat more complex perception of specific objects.

V5 (also referred to as MT) is further forward in the occipital lobe, and processes complex motion.

There seem to be two major pathways for visual information processing in the occipital lobe.  There is a "where?" path, from V1 to V2 to V3 and V5, that interprets location and motion in space.  And there is a "what?" path from V1 to V2 to V4 that determines the identity of an object.  There are additional areas whose functions are not yet known.

The Cingulate Gyrus

The cingulate gyrus sits below the rest of the cerebral cortex, up against the corpus callosum and partially covering lower areas such as the basal ganglia, the limbic system, and the thalamus.  Many people see it as the fifth lobe - others see it as part of the lobes above it, particularly the frontal lobe.  It is so intimately connected with the limbic system that it is sometimes called the limbic gyrus.  One of its major jobs is to keep your attention focused.  When it isn't functioning properly, as seems to happen in schizophrenia, you are unable to distinguish real voices from imaginary ones.

© Copyright 2006, C. George Boeree