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Brain Stimulation

Just as psychologists can learn about brain/behavior relationships by observing the effects of injury (which typically produces a deficit or absence of a skill) they can also learn from effects of brain stimulation.

The most common result of applying electrical current to the brain is (a) nothing, or (2) local seizure activity near the stimulation. However, in some cases, application of mild electrical current will stimulate a mental construction.

Cognitive constructions triggered by direct electrical stimulation are most common in epileptics. Perhaps seizure activity makes their brains are more accustomed to sudden electrical stimulation.

If a person with seizures has to undergo surgery to remove damaged brain tissue, the neurosurgeon will apply electrodes to stimulate near the area being removed. If there is a conscious response, the tissue is not removed, because it is functioning.

Organized, complex responses to direct brain stimulation are interesting to neuropsychologists. In such cases, electrical stimulation apparently activates a circuit or brain system. This gives us insight into how the brain is organized or divided up into functional sections, because the responses are location dependent.

Stimulated Movement

Luigi Galvani discovered in 1780 that an electrical spark would cause movement in a frog leg dissected from a frog. This was the first hint that electricity had something to do with biological systems, and it became famous.

Galvani's discovery was the inspiration for Mary Shelley's 1818 novel Frankenstein. Electricity was used to reanimate the monster. The Engineering and Technology History Wiki adds some detail:

...The notion of electricity and reanimation still lingered in the air when Mary Shelley penned her novel. Mary Shelley herself mentioned philosophical discus­sions between her husband, the poet Percy Shelley, and Lord Byron in 1816 on Luigi Galvani's experiments and how Galvanism suggested the possibility of reanimating the dead. ("Galvani and the Frankenstein Story," 2017)

Fritsch and Hitzig carried out the earliest systematic brain stimulation experiments on a mammal in 1870. They used a crude electrical apparatus to apply electricity to the exposed brain of a dog. They found that a mild electric current would cause the animal to lift its leg or make other bodily movements.

What were early studies by Fritsch and Hitzig?

One of the founding fathers of modern research into ESB (electrical stimulation of the brain) was Jose Delgado. He developed a radio transceiver for remote brain stimulation.

Delgado arranged a demonstration where a bull charged at him. With the push of a button, Delgado stopped the bull in its tracks. The stimulation probably disorganizing brain activity, momentarily stunning the bull.

Delgado did more scientifically interesting research by implanting electrodes in free-ranging monkeys. "Free-ranging" means the monkeys had freedom of movement. Delgado could trigger brain stimulation by remote control, using a radio transceiver.

What did Delgado find out by studying ESP in free-ranging monkeys?

Delgado found that stimulating a particular electrode (therefore a particular neural location) would trigger a specific motor fragment such as raising an arm. However, the meaning of that movement–how it was incorporated into the flow of behavior–depended upon what the monkey was doing at the time.

Stimulated Mental States

During the 1940s and early 1950s, a Canadian doctor explored "psychic effects" of stimulation during brain operations on humans. Wilder Penfield was a highly respected and specialized brain surgeon at the Montreal Neuro­psychiatric Institute. Hundreds of patients came to him specifically for brain surgery to relieve epilepsy.

Epilepsy is a word that describes a symptom, seizures, rather than a disease. Seizures can be caused by many things. Brain surgery is not usually needed, but in some cases where a damaged area of the brain causes seizures, surgery may help.

The fact that Penfield's patients were epileptic proved to be important. As noted above, only epileptic patients commonly respond to direct brain stimulation by having experiences they can report to a doctor.

During surgery, Penfield allowed his patients to regain consciousness so they could say whether they felt anything when a weak electrical current stimulated their exposed brains. If they did, it would indicate that the brain tissue at that location was still alive and functioning and should not be removed.

What did Penfield do during surgery?

The brain has no pain receptors itself, so the patient did not feel any pain from the electrical stimulation. Penfield put little numbered pieces of paper on the surface of the cortex to indicate where he had stimulated with electricity.

Sometimes stimulation produced vivid constructions that resembled memories. Here is one example:

A young man, J.T.,...who had recently come from his home in South Africa, cried out when the superior surface of his right temporal lobe was being stimulated: "Yes, Doctor! Yes, Doctor! Now I hear people laughing: my friends in South Africa."

After stimulation was over, he could discuss his...astonish­ment, for it had seemed to him that he was with his cousins at home where he and the two young ladies were laughing together. (Penfield, 1955)

Hallucinated Memories

Penfield believed he was activating real memories by stimulating the brain. He wrote a famous article titled, "A Permanent Record of the Stream of Consciousness" (Penfield, 1955) arguing that preservation of such arbitrary or random memories was evidence that nothing is ever forgotten and long-term memory preserves a permanent record of every experience.

This leap of logic was criticized by experimental psychologists such as Ulric Neisser and Elizabeth Loftus. They pointed out that even if arbitrary memories could be triggered by brain stimulation, that would be no reason to conclude all moments in life were stored permanently.

Penfield's theory had other problems. Some of the "memo­ries" were clearly hallucinatory. For example, one patient visualized herself giving birth.

She said she felt as though she was reliving the experience and watching it from above. Another patient reported hearing both sides of a private telephone conversation...from across the room.

None of the experiences reported by Penfield's patients could be verified as true and accurate memories. They just felt like real memories to the patients.

What do Penfield's "memory" findings really demonstrate?

Penfield's reports do not demonstrate a permanent record of the stream of consciousness. They demonstrate that the human brain, under certain conditions, can produce dreamlike constructions that feel like vivid memories.

Other Psychological Responses to Brain Stimulation

Following are some responses to brain stimulation Penfield documented.

Vocalization A person will make a moaning sound or other vocalization when the precentral gyrus at the top of the brain is stimulated.

Movement Leg or arm movements may occur when the motor cortex (the area represented in the homunculus) is stimulated. An "intelligent woman" stated, "my leg moved itself."

Sometimes the patient can suppress a movement triggered by brain stimulation. Other times stimulation results in "movement over which [the patient] has no control."

Music A musician heard a song from the musical Guys and Dolls when his temporal lobe was stimulated.

Auditory illusions A number of patients experienced a feeling that sounds in the environment were growing louder, or more far away, or occurring faster or slower.

Visual constructions One man saw "A man and a dog walking." Another saw "someone coming towards me as though he was going to hit me."

Spatial illusions Stimulation of the non-dominant hemisphere made things seem nearer, farther away, or distorted in space. Also common was the labyrinthine illusion, a feeling that the body had changed position in space.

Odors and tastes Some patients reported bitter tastes or disagree­able odors upon brain stimulation

Forced thoughts Patients often had "strange thoughts...difficult to explain" such as "a feeling that I had told somebody or other to do this or that."

Emotions Patients sometimes responded to brain stimulation with powerful feelings of nameless dread, fear, loneliness, remoteness, or disgust, other times with puzzlement or with laughter.

What other psychological responses did Penfield trigger with direct brain stimulation?

If the brain is involved in constructing the mind, it should not surprise us to find such a wide variety of experiences triggered by electrical stimulation. After all, every exper­ience is produced by the brain, in the opinion of modern neuro­scientists.

The Pleasure Centers

The discovery of "pleasure centers" in the brain is one of the more famous findings from brain stimulation research. It occurred by accident.

James Olds, working with Peter Milner, inserted an electrode into a rat's brain, aiming for the reticular system. The electrode curved off its intended course and landed in a different area, probably near the hypothalamus.

a rat with an electrode presses a bar
A rat with an electrode in the "pleasure center" presses a bar to get brain stimulation

Olds put the rat in a box and stimulated its brain whenever the rat approached a certain corner. He expected the rat to stay out of that corner, but instead Olds observed the rat was "coming back for more," acting as though the brain stim­ulation was pleasurable (Olds & Milner, 1954).

How were the pleasure centers discovered?

Further research showed that stimulation of areas in the limbic system produced pleasure in humans, too. Usually humans reported mild sensations.

Sometimes the stimulated sensations were sexual in nature; other times they were harder to describe. Individuals in pain or depressed were most likely to find electrical stimulation of the brain very pleasurable, perhaps as a contrast effect.

In the decades since Olds and Milner reported the existence of pleasure centers, scientists have identified the brain regions activated by feelings of triumph, euphoria, sexual pleasure. All involve dopamine, an important brain chemical we will discuss later in the chapter.

How do humans react when electrically stimulated in the "pleasure centers"? What chemical is associated with these brain areas?

Virtually all addictions, and even pleasurable feelings associated with religion, are accompanied by activation of dopaminergic (dopamine-using) pathways. This points to a hedonic (pleasure/pain) control system in mammalian animals. Apparently it can motivate a wide range of behaviors.


Galvani and the Frankenstein Story. (2017) Engineering Wiki [blog] Retrieved from: .

Loftus, E. F. & Loftus, G. R. (1980) On the permanence of stored information in the human brain. American Psychologist, 35, 409-420.

Olds, J. & Milner, P. (1954). Positive reinforcement produced by electrical stimulation of septal area and other regions of rat brain. Journal of Comparative and Physiological Psychology, 47, 419-427.

Penfield, W. (1955) The permanent record of the stream of consciousness. Acta Psychologica, 11, 47-69.

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