Pleasure Electrodes in the Brain (Dopamine 2)
- Hermes Solenzol
- Oct 10
- 7 min read
The Reward Pathway and Other Dopamine Neuronal Tracts
In the first article of this series, I discussed the idea of mental energy and how it appears in many spiritual traditions. In this one, I will start exploring the possible link between dopamine and mental energy by describing the function of the main dopamine neuronal pathways in the brain.
One way to understand the functioning of the brain is in terms of neuronal pathways. These are circuits of neurons that send their axons from one area of the brain to another, making contacts (synapses) with neurons in that region. Some neuronal pathways use a single neurotransmitter, in this case, we are going to explore the dopaminergic ones. Dopaminergic means that dopamine is the neurotransmitter used by a neuronal pathway.
‘Pleasure’ electrodes in the brain
It all started in 1953. James Olds and Peter Milner were postdoctoral fellows lab of the famous neuropsychologist Donald Hebb at McGill University, in Montreal. Their experiment consisted of implanting electrodes in the reticular formation of rats to study their sleep-wake cycle. They placed the rat in a large rectangular box and waited for the rat to be in a particular corner to pass current through the electrode. One of the rats kept coming back to that corner, as if it wanted to receive the stimulation (Olds and Milner, 1954; Olds, 1958). To check if this was true, they used a set-up called a Skinner box, in which rats can press a lever to activate the electrode themselves. What happened is that rats would press the lever several thousand times per hour. Given the choice between food, on the one hand, or pressing the lever, on the other hand, the rats chose to press the lever, even when they were hungry. Male rats preferred the lever over a sexually receptive female rat. Female rats abandoned their pups to go to press the lever.
In view of this, Olds named the region of the brain stimulated by the electrode pleasure centers in the brain. However, this idea was challenged later (Berridge and Kringelbach, 2015). Even Olds himself, in later books (Olds, 1977), recognized that there was no evidence that the rats felt pleasure when they stimulated the electrode.
The area stimulated by the electrodes implanted by Olds and Milner was the lateral hypothalamus (Berridge and Kringelbach, 2015). The hypothalamus is a region in the middle bottom of the brain that serves as a bridge between the brain and the body, connecting the brain with the endocrine system.
The psychiatrist Robert Heath took these experiments from the rat to human patients with schizophrenia, depression and other disorders (Heath, 1972). He found that the patients would avidly activate electrodes placed in a widespread ‘septal’ area that included the “septum, anterior hypothalamus, nucleus accumbens, ventral pallidum, ventromedial neostriatum, pyriform cortex and ventromedial neocortex” (Berridge and Kringelbach, 2015).
The most famous of Heath’s patients was B-19, a young man who Dr. Heath wanted to cure of his homosexuality by stimulating his brain in the supposedly ‘pleasure’ area located in the septum/nucleus accumbens (Heath, 1972). Although B-19 avidly self-simulated with this electrode, he never said that he experienced pleasure while doing so. And far from ‘curing’ his homosexuality, the electrode made him want more sex.
The reward pathway
Today, we know that the neuronal pathway stimulated by the electrodes is located in the ventral striatum, linking the ventral tegmental area (VTA) with the nucleus accumbens. It uses dopamine as a neurotransmitter. As I explained in a previous article, drugs that produce addiction does so by releasing dopamine in the nucleus accumbens to much higher levels than natural stimuli life sex, food or exercise.
This dopaminergic tract is called the mesolimbic pathway because it is located in the midbrain (hence meso) and is part of the limbic system, the areas of the brain that control emotions. However, it is better known as the reward pathway because it mediates what scientists call reward behavior: anything that an animal seeks. A reward is not necessarily pleasurable. It’s just something that the animal needs — like food, water, a mate, avoiding pain, or escaping the threat of a predator. A reward is anything that motivates the animal to act.
Today, even the name reward pathway is being questioned (Salamone and Correa, 2012) because there is much more to it than just craving some things and avoiding others. Its main role is to motivate us to do something, to keep us focused on a task, and to generate determination to keep sustained effort (Wanat et al., 2009; Salamone and Correa, 2012; Berke, 2018; Wise and Jordan, 2021). It’s more a motivation pathway. Motivation is similar to what I called mental energy in the previous article because when we are motivated we are ready to do some effort to achieve our goals and, when we are not, we feel passive and lazy.
The mesocortical pathway
However, the mesolimbic or reward pathway is not the only one that drives our motivation. There is another dopaminergic pathway that links the VTA with the brain cortex. It’s called the mesocortical pathway because it links the midbrain to the cortex. Its function is to maintain sustained effort and attention.
The mesocortical pathway stimulates the dorsolateral prefrontal cortex (PFC), which is where working memory resides, the desktop where we keep the things we are paying attention to in a given moment. The PFC also mediates cognitive flexibility; our ability to switch between mental contents; abstract reasoning; planning, and inhibiting spurious impulses.
The mesocortical pathway also activates the anterior cingulate cortex (ACC), which plays a crucial role in motivation, planning actions, attention, and detecting errors and conflicts.
Other dopaminergic pathways
All the current talk about dopamine centers in the reward pathway because it is the most relevant to the issues of addiction, motivation and mental energy. However, the reward and the mesocortical pathways are just two of the six major dopaminergic neuronal pathways in the brain. This shows that there isn’t just one single reservoir of dopamine in the brain. Instead, dopamine acts in different parts of the brain to fulfill a variety of functions.
Here is a brief description of the four other dopaminergic pathways.
The nigrostriatal pathway regulates movement and some forms of learning. It runs from the substantia nigra to the caudate nucleus and the putamen. The dopamine-containing neurons in the substantia nigra are gradually destroyed in Parkinson’s disease, causing the tremors and motor problems characteristic of this disease.
The hypothalamospinal tract goes from the hypothalamus to the spinal cord, where it controls sympathetic and parasympathetic neurons. Some of its neurons contain oxytocin, which regulates erection in males.
The two remaining dopaminergic pathways, the tuberoinfundibular and incertohypothalamic pathways, are key for the effects of dopamine on sexual function. Both of them are inside the hypothalamus, the part of the brain that controls body function in general and sexual responses in particular. In them, dopamine increases erection and ejaculation in males and sexual receptivity and orgasm in females. However, they are not responsible for sexual desire or pleasure. I will explore them in another article.
The tuberoinfundibular pathway goes from the arcuate nucleus (also called the infundibular nucleus) to the median eminence, which releases hormones into the pituitary gland, which in turn releases hormones into the blood to regulate the endocrine system.
The incertohypothalamic pathway goes from the zona incerta, an area below the thalamus also called A14, to the paraventricular nucleus. Besides sexual behavior, it regulates fear responses and the autonomic nervous system.
A seventh dopaminergic pathway goes from the A11 nucleus, near the thalamus, to the spinal cord, where it controls pain.
The logic behind that idea that sex depletes mental energy
The idea that sex depletes mental energy follows this logic:
Dopamine is essential to activate the reward and mesocortical pathways, which generate motivation and sustain attention and effort — what I have called mental energy.
Sex is a powerful natural reward, so it releases dopamine in the reward pathway.
Too much sex (porn, masturbation) depletes dopamine in the reward pathway, so there is not enough to sustain mental energy.
The key question is in step 3. Is it true that sex depletes dopamine in the reward pathway? Is this depletion enough to have a noticeable effect on mental energy?
There is a lot of confusion about what dopamine depletion really means. Sadly, this is perpetuated by the careless use of this expression in many scientific papers.
We get the image that there is a reservoir of dopamine in the brain that leaks dopamine every time we experience pleasure. If the brain doesn’t manage to replenish the reservoir fast enough, we are left without dopamine and, therefore, without energy.
However, there is no reservoir of dopamine. This is not how neurotransmitters work.
In the next article, I will describe the dopamine synapse to explore whether dopamine depletion really occurs in the reward pathway. Can too much sex or pleasure decrease the dopamine that sustain our mental energy?
References
Berke JD (2018) What does dopamine mean? Nat Neurosci 21:787–793.
Berridge Kent C, Kringelbach Morten L (2015) Pleasure Systems in the Brain. Neuron 86:646–664.
Heath RG (1972) Pleasure and brain activity in man. Deep and surface electroencephalograms during orgasm. J NervMentDis 154:3–18.
Olds J (1958) Self-stimulation of the brain; its use to study local effects of hunger, sex, and drugs. Science 127:315–324.
Olds J (1977) Drives and reinforcements: Behavioral studies of hypothalamic functions. New York: Raven Press.
Olds J, Milner P (1954) Positive reinforcement produced by electrical stimulation of septal area and other regions of rat brain. J Comp Physiol Psychol 47:419–427.
Salamone JD, Correa M (2012) The mysterious motivational functions of mesolimbic dopamine. Neuron 76:470–485.
Wanat MJ, Willuhn I, Clark JJ, Phillips PE (2009) Phasic dopamine release in appetitive behaviors and drug addiction. Curr Drug Abuse Rev 2:195–213.
Wise RA, Jordan CJ (2021) Dopamine, behavior, and addiction. J Biomed Sci 28:83.
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