The putamen is a round structure located at the base of the forebrain. The
putamen and caudate nucleus together form the dorsal striatum. It is also one
of the structures that comprises the basal ganglia. Through various pathways,
the putamen is connected to the substantia nigra and globus pallidus.
The main function of the putamen is to regulate movements and influence various
types of learning. It employs GABA, acetylcholine, and enkephalin to perform
its functions. The putamen also plays a role in degenerative neurological
disorders, such as Parkinson's disease. History
The word "putamen" is from Latin, referring to that which "falls off in
pruning", from "putare", meaning "to prune, to think, or to consider". It is
pronounced pyu-ta'men. Until recently, very few studies were
conducted that were focused specifically on the putamen. However, many studies
have been done on the basal ganglia and the interactions among the brain
structures it comprises. In the 1970s, the first single unit recordings were
done with monkeys monitoring pallidal neuron activity related to movement.
Anatomy The putamen is a structure in the
forebrain. Along with the caudate nucleus it forms the dorsal striatum.
The caudate and putamen contain the same types of neurons and circuits - many
neuroanatomists consider the dorsal striatum to be a single structure,
divided into two parts by a large fiber tract, the internal capsule, passing
through the middle. The putamen, together with the globus pallidus, makes
up the lenticular nucleus. The putamen is the outer most portion of the basal
ganglia. These are a group of nuclei in the brain that are interconnected with
the cerebral cortex, thalamus, and brain stem. Basal ganglia include the dorsal
striatum, substantia nigra, nucleus accumbens, and the subthalamic nucleus.
In mammals, the basal ganglia are associated with motor control,
cognition, emotions, and learning. The basal ganglia are located on the left
and right sides of the brain, and have rostral and caudal divisions. The
putamen is located in the rostral division as part of the striatum. The
basal ganglia receive input from the cerebral cortex, via the striatum.
The putamen is interconnected with the following structures:
= Caudate Nucleus = The caudate works with the putamen to
receive the input from cerebral cortex. They can be considered the "entrance" to
the basal ganglia. The nucleus accumbens and medial caudate receive input from
frontal cortex and limbic regions. The putamen and caudate are jointly
connected with the substantia nigra, but most of their output goes to the globus
pallidus. = Substantia Nigra =
The substantia nigra contains two parts: the substantia nigra pars compacta and
the substantia nigra pars reticulata. The SNpc obtains input from the putamen
and caudate, and sends information back. The SNpr also obtains input from the
putamen and caudate. However, it sends the input outside the basal ganglia to
control head and eye movements. The SNpc produces dopamine, which is crucial for
movements. The SNpc is the part that degenerates during Parkinson's disease.
= Globus Pallidus = The globus pallidus contains two parts:
the globus pallidus pars externa and the globus pallidus pars interna. Both
regions acquire input from the putamen and caudate and communicate with the
subthalamic nucleus. However, mostly the GPi sends the inhibitory output from the
basal ganglia to the thalamus. The GPi also sends a few projections to parts of
the midbrain, which have been assumed to affect posture control.
Physiology = Types of Pathways =
In order to control movement, the putamen must interact with the other
structures that make up the basal ganglia. These include the caudate
nucleus and globus pallidus. These two structures, along with the putamen,
interact through a series of direct and indirect inhibitory pathways. The direct
pathway consists of two inhibitory pathways from the putamen to the
substantia nigra and the internal region of the globus pallidus. This pathway
uses the neurotransmitters dopamine, GABA and substance P. The indirect
pathway consists of three inhibitory pathways that go from the putamen and
caudate nucleus to the external region of the globus pallidus. This pathway
uses dopamine, GABA and enkephalin. When there is interplay between the direct
and indirect pathways, involuntary movements occur.
= Dopamine = One of the main neurotransmitters that
is regulated by the putamen is dopamine. When a cell body of a neuron fires an
action potential, dopamine is released from the presynaptic terminal. Since
projections from the putamen and caudate nuclei modulate the dendrites of the
substantia nigra, the dopamine influences the substantia nigra, which
affects motor planning. This same mechanism is involved in drug addiction.
In order to control the amount of dopamine in the synaptic cleft, and the
amount of dopamine binding to post synaptic terminals, presynaptic
dopaminergic neurons function to reuptake the excess dopamine.
= Other Neurotransmitters = The putamen also plays a role in
modulation of other neurotransmitters. It releases GABA, enkephalin, substance
P, and acetylcholine. It receives serotonin and glutamate. The majority of
these neurotransmitters play a role in motor control.
Function: Motor Skills While the putamen has many functions, it
has been concluded that it has no specific specialization. However, since
the putamen is interconnected with so many other structures, it works in
conjunction with them to control many types of motor skills. These include
controlling motor learning, motor performance and tasks, motor
preparation, specifying amplitudes of movement, and movement sequences.
Some neurologists hypothesize that the putamen also plays a role in the
selection of movement and the "automatic" performance of previously
learned movements. In one study it was found that the
putamen controls limb movement. The goal of this study was to determine whether
particular cell activity in the putamen of primates was related to the direction
of limb movement or to the underlying pattern of muscular activity. Two
monkeys were trained to perform tasks that involved the movement of loads. The
tasks were created so that movement could be distinguished from muscle
activity. Neurons in the putamen were selected for monitoring only if they
were related both to the task and to arm movements outside the task. It was shown
that 50% of the neurons that were monitored were related to the direction
of movement, independent of the load. Another study was done to investigate
movement extent and speed using PET mapping of regional cerebral blood flow
in 13 humans. Movement tasks were performed with a joystick-controlled
cursor. Statistical tests were done to calculate the extent of movements and
what regions of the brain the movements correlate to. It was found that
"increasing movement extent was associated with parallel increases of
rCBF in bilateral basal ganglia and ipsilateral cerebellum." This not only
shows that the putamen affects movement but it also shows that the putamen
integrates with other structures in order to perform tasks.
One study was done in order to specifically investigate how the basal
ganglia influences the learning of sequential movements. Two monkeys were
trained to press a series of buttons in sequence. The methods used were designed
to be able to monitor the well-learned tasks versus the new tasks. Muscimol was
injected into various parts of the basal ganglia, and it was found that "the
learning of new sequences became deficient after injections in the
anterior caudate and putamen, but not the middle-posterior putamen." This
shows that different areas of the striatum are utilized when performing
various aspects of the learning of sequential movements
Role in learning In many studies, it has become apparent
that the putamen plays a role in many types of learning. Some examples are
listed below: = Reinforcement and implicit learning =
Along with various types of movement, the putamen also affects reinforcement
learning and implicit learning. Reinforcement learning is interacting
with the environment and catering actions to maximize the outcome.
Implicit learning is a passive process where people are exposed to information
and acquire knowledge through exposure. Although the exact mechanisms are not
known, it is clear that dopamine and tonically active neurons play a key role
here. Tonically active neurons are cholinergic interneurons that fire
during the entire duration of the stimulus and fire at about 0.5-3
impulses per second. Phasic neurons are the opposite and only fire an action
potential when movement occurs. = Category Learning =
One particular study used patients with focal lesions on the basal ganglia due
to stroke in order to study category learning. The advantage to using these
types of patients is that dopaminergic projections to the prefrontal cortex are
more likely to be intact. Also, in these patients, it is easier to relate
specific brain structures to function because the lesion only occurs in a
specific place. The goal of this study was to determine whether or not these
lesions affect rule-based and information-integration task learning.
Rule-based tasks are learned via hypothesis-testing dependent on working
memory. Information-integration tasks are ones wherein the accuracy is
maximized when information from two sources are integrated at a
pre-decisional stage, which follows a procedural-based system.
Seven participants with basal ganglia lesions were used in the experiment,
along with nine control participants. It is important to note that the caudate
was not affected. The participants were tested for each type of learning during
separate sessions, so the information processes would not interfere with each
other. During each session, participants sat in front of a computer screen and
various lines were displayed. These lines were created by using a
randomization technique where random samples were taken from one of four
categories. For ruled-based testing, these samples were used to construct
lines of various length and orientation that fell into these four separate
categories. After the stimulus was displayed, the subjects were asked to
press 1 of 4 buttons to indicate which category the line fell into. The same
process was repeated for information-integration tasks, and the
same stimuli were used, except that the category boundaries were rotated 45°.
This rotation causes the subject to integrate the quantitative information
about the line before determining what category it is in.
It was found that subjects in the experimental group were impaired while
performing rule-based tasks, but not information-integration ones. After
statistical testing, it was also hypothesized that the brain began using
information-integration techniques to solve the rule-based learning tasks.
Since rule-based tasks use the hypothesis-testing system of the brain,
it can be concluded that the hypothesis-testing system of the brain
was damaged/weakened. It is known that the caudate and working memories are
part of this system. Therefore, it was confirmed that the putamen is involved
category learning, competition between the systems, feed-back processing in
rule-based tasks, and is involved in the processing of pre-frontal regions. Now
it is known that not only the basal ganglia and caudate affect category
learning. Role in "hate circuit"
Recent, tentative studies have suggested that the putamen may play a role in the
so-called "hate circuit" of the brain. A recent study was done in London by the
department of cell and developmental biology at University College London. An
fMRI was done on patients while they viewed a picture of people they hated
and people who were "neutral". During the experiment, a "hate score" was
recorded for each picture. The activity in sub-cortical areas of the brain
implied that the "hate circuit" involves the putamen and the insula. It has been
theorized that the "putamen plays a role in the perception of contempt and
disgust, and may be part of the motor system that's mobilized to take action."
It was also found that the amount of activity in the hate circuit correlates
with the amount of hate a person declares, which could have legal
implications concerning malicious crimes.
Role in Transgender Individuals The putamen was found to have
significantly larger amounts of grey matter in male to female transgender
individuals compared to the putamen of a typical cisgender male. This possibly
suggests that a fundamental difference in brain composition may exist between
trans women and cis men. Pathology
= Parkinson's disease = After discovering the function of the
putamen, it has become apparent to neurologists that the putamen and basal
ganglia play an important role in Parkinson's disease and other diseases
that involve the degeneration of neurons.
Parkinson's disease is the slow and steady loss of dopaminergic neurons in
substantia nigra pars compacta. In Parkinson's disease the putamen plays a
key role because its inputs and outputs are interconnected to the substantia
nigra and the globus pallidus. In Parkinson's disease the activity in
direct pathways to interior globus pallidus decreases and activity in
indirect pathways to external globus pallidus increases. Together these
actions cause excessive inhibition of the thalamus. This is why Parkinson’s
patients have tremors and have trouble performing voluntary movements. It has
also been noted that Parkinson’s patients have a difficult time with
motor planning. They must think about everything they do and cannot perform
instinctive tasks without focusing on what they are doing.
= Other diseases and disorders = The following diseases and disorders are
linked with the putamen: Cognitive decline in Alzheimer's disease
Huntington's disease Wilson's disease
Dementia with Lewy bodies Corticobasal degeneration
Tourette syndrome Schizophrenia
Depression Attention Deficit Hyperactivity Disorder
Chorea Obsessive-Compulsive Disorder
Other anxiety disorders In other animals
The putamen in humans is similar in structure and function to other animals.
Therefore, many studies on the putamen have been done on animals, as well as
humans. Additional images
See also Lentiform nucleus
References External links
Stained brain slice images which include the "putamen" at the BrainMaps project
Anatomy diagram: 13048.000-2 at Roche Lexicon - illustrated navigator,
Elsevier Diagram at uni-tuebingen.de
Atlas image: eye_38 at the University of Michigan Health System - "The Visual
Pathway from Below"