The Brain Pleasure and Pain

the reward circuit and the punishment circuit

Together these two circuits form the behavior approach system to motivation.

Pleasure serves as a reward for the body having undergone the vital functions required to stay alive.

Things like eating, drinking, responding to aggression, and reproducing all elicit pleasure as motivation to undergo these necessary life functions.

The reward circuit is the interconnected loop in the brain that coordinates all the various brain structures that deal with reward and pleasure.

The ventral tegmental area and the nucleus accumbens

Other various brain structures involved in the circuit include the septum, the amygdala, the prefrontal cortex, and the thalamus.

The ventral tegmental area (VTA) is located in the very center of the brain; it receives information about how human needs are being satisfied and communicates this information to other structures of the brain.

dopamine

The ventral tegmental area sends dopamine to the following structures:

1. The nucleus accumbens

2. The amygdala

3. The septum

4. The prefrontal cortex

An increase in dopamine causes the current behavior to be rewarded and reinforced.

The nucleus accumbens is a bundle of neurons located slightly anterior to the hypothalamus; it receives reward information from the VTA, activates motor functions, and further relays the information to the prefrontal cortex.

When stimulated by dopamine from the ventral tegmental area, the prefrontal cortex responds by increasing conscious awareness and attention.

The medial forebrain bundle (MFB) connects the various structures involved in the reward circuit; it helps to strengthen the association between the structures in order to promote repetition of the action.

The punishment circuit enables humans to cope with unpleasant situations and avoid future painful experiences.

The punishment circuit is activated by aversive stimuli that also initiate the body’s fight or flight response.

The brain structures involved in the punishment circuit are the following:

1. The thalamus

2. The hypothalamus

3. The grey matter surrounding the cerebral aquaduct

4. The amygdala

5. The hippocampus

acetylcholine

Acetylcholine causes the anterior pituitary gland to secrete adrenocorticotropic hormone (ACTH).

ACTH stimulates the secretion of epinephrine from the adrenal glands, in order to prepare the body for fight or flight.

The behavioral inhibition system (BIS) is activated when both fight and flight seem ineffective, and the only effective response to ensure survival is to submit passively.

The BIS causes an overall inhibition of behavior, thereby working against the behavioral action system of the reward and punishment circuits.

the nucleus accumbens

The level of dopamine increases.

An increased level of dopamine has a notable effect on the brain’s reward circuit.

Drugs target receptors on the VTA that cause an increase in dopamine production.

The prefrontal cortex modulates planning and motivating action and is controlled by dopamine. When drugs initiate an increase in dopamine, the profrontal cortex is even more stimulated, causing a rise in motivation.

The locus coeruleus plays an important role in drug addiction, as it is stimulated when there is a lack of the drug, and causes the addict to do anything possible to obtain the feelings associated with the drug.

1. The amygdala

2. The hippocampus

3. The insular cortex

No, the brain does not contain a single pain center. Instead, there appears to be a pain matrix, whereby many brain structures are interconnected and coordinated.

The purpose of pain is to make a person aware that his/her body is damaged or is about to be damaged, allowing them to change his/her actions.

Nociception is the sensory process that produces nerve signals that are sent to the brain as pain.

A nociceptor is a dense network of free nerve endings that function as the sensory receptor for pain.

Pain is a negative sensation felt in a particular part of the body that results from nociception.

Nociception and pain are not the same; nociception is the process by which humans feel pain.

The reticular formation is involved with the alertness associated with pain; it alters heart rate, blood pressure, respiration rate, and other bodily functions affected by pain.

The VPL projects axons to the somatosensory cortex, helping to locate and determine the intensity of pain. It also functions to relay the sense of touch to the cortex.

The medial portion of the thalamus projects axons to the motor cortex areas of the frontal lobe, and therefore associates pain with motor and emotional reactions.

The intralaminar nuclei of the thalmus are involved with the alertness response of pain and produce the negative emotional components and the behavioral responses of pain.

The intralaminar nuclei send axons to the limbic system.

The primary somatosensory cortex receives axons from the VPL of the thalamus and discriminates the various properties of pain.

The primary somatosensory cortex can send axons to the seconday somatosensory cortex for further pain processing.

The secondary somatosensory cortex receives axons from the primary somatosensory cortex and the thalamic nuclei; it further processes pain by recognizing and associating it with past pain.

Acute pain is an immediate sensation of pain that results from a specific, highly localized, bodily injury.

Acute pain can last anywhere from a few seconds to months, but in all cases the pain eventually fades as the illness is cured or the body heals.

Chronic pain is a disease in which pain does not have any connection to a previous injury, and instead is a result of a variety of abnormal cellular processes.

Chronic pain can be intermittent or constant, and is extremely debilitating, vastly affecting one's quality of life.a

Neurogenic pain results from damage or disease directly affecting the nerves of the nociceptive pathway.

Sensations associated with neurogenic pain include hyperalgesia and allodynia.

Hyperalgesia is a sensation associated with neurogenic pain in which a stimulus causes much more pain than it normally would.

Allodynia is a sensation associated with neurogenic pain in which extremely light stimuli cause severe pain.

Psychogenic pain is a physical pain that has no associated physical injury or disease; it is often a result of mental, emotional, or behavioral factors.