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OCD, Dopamine, and the Nucleus Acumbens

It is easy to mistakenly assume that behaviors seen in OCD (including grooming disorders) and Tourette syndrome are not goal directed—that they are senseless and meaningless. It may even feel senseless and meaningless to the person afflicted with symptoms. But there is a purpose behind the behavior—to reduce frustration and/or to release pent up SEEKING behavior, whether one is motivated to seek out attachments or resources. In "The Primate Basal Ganglia: Parallel and Integrative Networks" (2003), Suzanne N. Haber explains that "The basal ganglia [corpus striata complex] and frontal cortex operate together to execute goal directed behaviors." It is difficult to sum up this cooperative effort. Here, some of Haber's concepts are combined with :

Amygdala-labeled emotions combine with dopamine-powered motivation to produce an impetus that the frontal cortex shapes via cognition to organize and plan strategy to shape motor output.










Obsessions and compulsions—symptoms and triggers:

We can begin to better understand how dysfunctions occur when we better understand how normal behavior is engendered.

Regarding normal, primate behavior, including human behavior, Haber writes:

The components of the frontal cortex that mediate these behaviors are reflected in the organization, physiology, and connections between areas of frontal cortex and in their projections through basal ganglia circuits. This comprises a series of parallel pathways. However, this model does not address how information flows between circuits thereby developing new learned behaviors (or actions) from a combination of inputs from emotional, cognitive, and motor cortical areas. Recent anatomical evidence from primates demonstrates that the neuro-networks within basal ganglia pathways are in a position to move information across functional circuits. Two networks are: the striato-nigral-striatal network and the thalamo-cortical-thalamic network. Within each of these sets of connected structures, there are both reciprocal connections linking up regions associated with similar functions and non-reciprocal connections linking up regions that are associated with different cortical basal ganglia circuits. Each component of information (from limbic to motor outcome) sends both feedback connection, and also a feedforward connection, allowing the transfer of information. Information is channeled from limbic, to cognitive, to motor circuits. Action decision-making processes are thus influenced by motivation and cognitive inputs, allowing the animal to respond appropriate to environmental cues.

In this section, we will discuss and clarify the structures and neurocircuitry involved in the parallel circuits Haber describes above.

Brain directions planes sections directions

On this page,several images of coronal sections of human brain have been borrowed from a Washington University in St. Louis (WUStL) Neuroscience Tutorial that is no longer internet accessible. Diana Weedman Molavi created the tutorial. The images originate from the collections of Joel Price, Harold Burton, and David Van Essen, Department of Anatomy and Neurobiology, WUStL. In these coronal sections, the myelin part of the tissue has been stained. So instead of its natural white appearance, in these particular images, the myelin appears black. The diagram to the right depicting coronal, horizontal, and saggital planes is also from the WUStL tutorial. Molavi writes: "Coronal sections are the easiest to visualize, because their orientation is just like looking face-on at another person. Up is up and down is down." The coronal images below correspond in orientation to the color-labeled illustration of the corpus striata complex used in OCD and the corpus striata complex (basal ganglia).

The brain's development of emotive and motor functions:

Human Brain Amygdala

In Part 1 of CorticalBrain.com, in The amygdala, stress, OCD, and PTSD, we discuss incentive salience with the help of authors Ramachandran and Oberman. The authors describe how the amygdalae create a salience landscape, a kind of directory that encodes the emotional significance of everything in an individual's environment. The emotion-packed interconnections between the amygdalae and the corpus striata complex figure prominently in the development of behavior including dysfunctional symptoms. In "Neuropsychiatry of the Basal Ganglia" (2002), H.A. Ring and J. Serra-Mestres explain the important anatomical links between structures governing emotive functions (the amygdala and hippocampus) and structures prompting subsequent motor functions (the corpus striata complex, also called the basal ganglia). To develop the material excerpted below, Ring and Serra-Mestres cite Andre Parent's and Malcolm B. Carpenter's book, Carpenter's Human Neuroanatomy.

The basal ganglia develop as part of the telencephalon, from the basal region of the mantle layer of the primitive telencephalic vesicle and the amygdala complex develops from the same tissue mass as the caudate nucleus. These findings emphasise that there are important links between parts of the brain that have classically been considered to be related to emotional functioning [amygdala] and parts of the brain that have in the past been considered to play a part largely in motor functions [basal ganglia/corpus striata].

Regarding the telencephalon, a forebrain structure, you may wish to review a previous discussion of brain development in Part 1 of CorticalBrain.com called Neural tube brain organization. My take on the observations of Ring and Serra-Mestres is that both emotive and motor functions are essential components of our being. Without one or the other, we are neither human, primate, nor mammal.

The globus pallidus and nucleus accumbens:

In the image below from the Washington University in St. Louis Neuroscience Tutorial, you can see the globus pallidus labeled "GP externa" and "GP interna."

brain globus pallidum brain globus pallidum

As we discuss in OCD and the corpus striata complex (basal ganglia), the corpus striata complex, which includes the globus pallidus, has been associated with obsessive and compulsive symptoms as well as movement disorders. In "Obsessive-Compulsive and other Behavioural Changes with Bilateral Basal Ganglia Lesions: A Neuropsychological, Magnetic Resonance Imaging and Positron Tomography Study" (1989), D. Laplane et al. report on eight patients who "shared the combination of bilateral basal ganglia lesions and a frontal lobe-like syndrome." The authors write: "Some patients showed stereotyped activities with compulsive and obsessive behaviour which were sometimes highly elaborate in pattern. … The lesions appeared to be confined to the lentiform nuclei [putamen and globus pallidus], particularly affecting the pallidum [globus pallidus], although there was generalized brain atrophy in 2 cases."

From the coronal orientation, the globus pallidus is situated more deeply within the brain than the nucleus accumbens. In the image below, the putamen and nucleus accumbens on the left partially block the view of the more deeply recessed globus pallidus. This image is from the Temple University School of Medicine's Department of Anatomy and Cell Biology website. Marvin Sodicoff created the site with adaptations from Rod Bain, Andrew Blum, and David Ni. the labeling is added here. To see an unlabeled version and to practice identifying structures, click on the image.

brain nucleus accumbens

Like the globus pallidus, the nucleus accumbens is a component of the larger corpus striata complex. Both the nucleus accumbens and the caudate-putamen project to the globus pallidus, also called the pallidum. In "Neuropsychiatry of the Basal Ganglia" (2002), Ring and Serra-Mestres clarify some anatomical issues. The first involves the term striatum. The caudate nucleus and putamen, both structures of the corpus striata complex, are together sometimes called the striatum. The nucleus accumbens is considered part of the ventral striatum; in other words the nucleus accumbens is in the lower part of the overall structure. The nucleus accumbens has both a core area and a shell area; these areas have different functions, neural projections, and morphologies (organization and appearance).

In the chapter on mammals in The Central Nervous System of Vertebrates (1998), Voogd, Nieuwenhuys, Van Dongen, and Ten Donkelaar write: "Because the nucleus accumbens receives massive projections from the hippocampal formation and the amygdala, both essential components of the limbic system, this cell mass has been hypothesized to constitute the functional interface between the limbic and the motor system (Mogenson et al. 1980; Mogenson 1984; Hooks and Kalivas 1995)."

"The nucleus accumbens, which lies within the basal ganglia, may be a primary ganglion for the organization of action within the brain," writes Jay Schulkin in Effort: A Behavioral Neuroscience Perspective on the Will (2007). "Some time ago, Nauta (1961; Kelley, Domesick, & Nauta, 1982; Nauta & Domesick, 1982) suggested that the nucleus accumbens is an important link between the amygdala and motivation for the organization of action (Mogenson & Huang, 1973). Translation of motivational output from the amygdala to the behavioral outputs of the basal ganglia takes place via the connectivity to the nucleus accumbens (Kelley, 1999; Mogenson, Jones and Yim, 1980; Swanson, 2003)."

The one question regarding Schulkin's remarks above relates to his reference to the amygdala's "motivational output." it is understood that motivation to come primarily from the SEEKING system—the VTA to nucleus accumbens pathway (often called the mesolimbic dopamine pathway). One could say that the amygdalae ascribe salience and thereby shape and label dopamine-produced motivation or dopamine input to the nucleus accumbens. In discussing the SEEKING system, we have already discussed how neurons in the VTA produce dopamine that is released into the nucleus accumbens. So we will not revisit the SEEKING system here. For review, see Dopamine action, synthesis, and pathways and The Brain's SEEKING System. Once read all of Schulkin's book to clarify these issues.

The brain's emotive-motivational-motor interchange:

The corpus striata complex manages neurosignaling from several distinct sources and serves as a sort of interchange between emotive, motivational, and motor neurosignaling. Here, we are using the term motivational neurosignaling to mean the mesolimbic dopamine pathway. We are using the term motor neurosignaling to mean the nigrostriatal pathway. For review of the nigrostriatal pathway, you may want to take a look at Parkinson's Disease and dopamine.

Integrated, balanced emotive-motivational-motor neurosignaling eventually communicates to cortical regions that manage movement—the motor cortex. To oversimplify, senses/feelings prompt emotion that combines with motivation and, with cognitive/cortical influence, prompts movement/behavior. Needless to say, imbalances within the system can cause dysfunctional behavior or movement.

Emotive Function: Signals from the hippocampus and amygdala (often called limbic structures) flow into what is called the ventral striatum. As we discuss above, this area is the lower portion of the overall striatal structure and includes the nucleus accumbens. Incoming amygdala and hippocampus neurosignaling to the nucleus accumbens relate to the feelings and memories associated with what we see, hear, smell, taste, and touch in the world, including the feelings and memories associated with our interactions with other beings. In Part 1 of CorticalBrain.com, in Subcortical Brain Structures, Stress, Emotions, and Mental Illness, we discuss the memory forming role of hippocampus and the salience forming role of the amygdala, which in turn influence the hypothalamus and the autonomic nervous system. As Robert M. Sapolsky observes in Monkeyluv and Other Essays on Our lives as Animals (2005): "Sometimes, all you need to do is think a thought and you change the functioning of virtually every cell in your body."

Motivational Function: Again, here we are using the term motivational neurosignaling to mean the mesolimbic dopamine pathway and the SEEKING system as Jaak Panksepp defines it in Affective Neuroscience: The Foundations of Human and Animal Emotions (1998).

Human Brain Dopamine Neurons

Motor function: The image to the right is credited to Donato DiMonte of the Parkinson's Institute and links to Cindy Lawler's succinct article regarding the epidemiology of Parkinson's Disease. The image depicts in vitro dopamine neurons (in other words these particular neurons are being maintained in an artificial environment). The upper portion of the overall striatal structure, called the dorsal striatum or caudate-putamen complex receives dopamine signaling from neurons similar to these in the nigrostriatal pathway. This pathway is directly associated with movement. Parkinson's Disease results when dopamine-producing neurons are depleted in the substantia nigra, where the nigrostriatal pathway originates (see Parkinson's Disease and dopamine).

In addition to basic movement, in "The role of nucleus accumbens dopamine in motivated behavior: a unifying interpretation with special reference to reward-seeking," Satoshi Ikemoto and Jaak Panksepp explain that "The nigro-striatal DA [dopamine] system appears to be a key structure involved in habit formation (stimulus-response learning)." In making this conclusion, Ikemoto and Panksepp cite, among others, N.M. White's "Mnemonic functions of the basal ganglia" (1997).

Before moving ahead to White's work, we will review some concepts related to memory. The New Oxford American Dictionary on my Apple MacBook defines the adjective mnemonic thus: "aiding or designed to aid the memory." There are different kinds of memory. Declarative memory relates to remembering facts and events. According to Wikipedia, "Procedural memory is our memory for how to do things. When needed, procedural memories are automatically retrieved and utilized for the execution of the step-by-step procedures involved in both cognitive and motor skills; from tying shoes to flying an airplane. This process occurs without the need for conscious control or attention. Procedural memory is a type of long-term memory and more specifically a type of implicit memory." And, "Implicit memory is a type of memory in which previous experiences aid in the performance of a task without conscious awareness of these previous experiences." Here, we are talking more about procedural and implicit memory. In White's "Mnemonic functions of the basal ganglia," the author writes:

A synthesis of older and recent work on mnemonic functions of the basal ganglia in rats, monkeys and humans emphasizes a reciprocal relationship of the caudate nucleus and putamen with the cerebral cortex, which mediates the memory of consistent relationships between stimuli and responses (sometimes called habits) that often involve relationships between the individual and its environment (egocentric memory). Evidence at several levels of analysis (including neuroplastic synaptic changes, activity of single neurons, and behavioral changes caused by lesions or neurochemical manipulations) implicate dopamine release from nigro-striatal neurons in the reinforcement, or strengthening, of neural representations in the basal ganglia.

In a 1984 article in Nature titled "Weaver mutation has differential effects on the dopamine-containing innervation of the limbic and nonlimbic striatum," Suzanne Roffler-Tarlov and Ann M. Graybiel establish a morphological distinction between corpus striata brain areas associated with emotive function and corpus striata brain areas associated with motor function. "The nucleus accumbens-olfactory tubercle region and abutting caudoputamen (together called the 'ventral' or 'limbic' striatum) are characteristically related to limbic parts of the forebrain, whereas the large remainder of the caudoputamen (the 'dorsal' or 'non-limbic' striatum) is most closely related to sensorimotor regions."

To sum up, the corpus striata complex is where sensory, emotive, motivational, motor, and cognitive neurosignaling converge. One small thing gone wrong in the corpus striata complex could possibly prompt the troubling OCD or Tourette syndrome symptoms where one is seemingly disconnected from one's will.

Next-> The brain's cortical-subcortical circuits:

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