Lobes of the Brain

Lobes are large areas of the cerebral cortex bounded by fissures in the brain. The occipital [ok-SIP-it-al] lobe is at the back of the brain. It is largely specialized for vision. Stimulating here in the primary visual cortex with a weak electric current causes a person to see phosphenes—little glowing lights.

What visual event is caused by stimulation of the occipital lobe?

Once there was hope that implanting an array of electrodes in the occipital lobe would allow messages to be flashed to blind people like words on an electronic billboard. However, it turned out that the phosphenes created by stimulating a particular area of cortex did not always occur in the same location of the visual field, so those hopes vanished. More complex visual areas extend beyond the primary visual cortex into the temporal lobe on the side of the brain. Stimulating this area can result in visual hallucinations. Damage along the lower side of the temporal lobe can cause visual agnosia -the inability to recognize objects.

Major lobes on a brain "facing left" (frontal lobes to left)

The parietal (par-EYE-it all) lobe is the middle area of the brain. Parietal cortex in the right hemisphere is usually devoted to spatial processing: the type of talent used to figure out maps or find one's way around a complex environment.

Where is the temporal lobe located? The frontal lobe? Where are the prefrontal areas?

The temporal lobe is on the side of the brain, below a major fold called the lateral or Sylvian fissure (right above the word "Auditory" in the diagram). The temporal lobe contains not only the secondary visual areas but also some tissue devoted to hearing. Stimulating it on the upper surface can result in the déjà vu sensation that we discuss later in this chapter and again in Chapter 4.

The frontal lobes are in the front of the brain. The frontal lobe is larger in humans than any other animal. The prefrontal areas right behind the eyes are involved in executive functions such as selective attention and task management (Smith & Jonides, 1999). These are some of the most complex and distinctively human thought processes. When the frontal lobes are damaged or isolated from the rest of the brain in the operation called the lobotomy people lose their ability to plan for the future and perform creative activities.

What is located on either side of the central fissure? What are "motor functions"?

Running from the top of the head down toward the ear is the central fissure or fissure of Rolando. On both sides of this central fissure are areas specialized for sensory inputs (inputs from the sense organs) and motor outputs (outputs to the muscles). The area behind the central fissure is called the sensory cortex, and the area in front is called the motor cortex. These labels are from the 1800s. Today's scientists know that both areas, the so-called sensory cortex and motor cortex, contain sensory and motor functions. Both areas are involved in receiving inputs from the senses (sensory functions), and both are involved in sending outputs to the muscles (motor functions).

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Copyright © 2007 Russ Dewey