The basal ganglia

"... those dark foundations of the brain... " Kinnier Wilson (1925).

The basal ganglia (BG) ^{[4, 54, 91]} are a group of richly interconnected subcortical nuclei. They appear gray because they primarily contain neuronal cell bodies. The basal ganglia play a vital role in motor control ^[53].

There are four primary nuclei: the striatum ^[80], the pallidum, the subthalamic nucleus, and the substantia nigra (locus niger) ^[4] , in addition to a few other brain structures whose inclusion in the basal ganglia is debated. (Some authors even include the thalamus among the basal ganglia ^{[39, 66]} , but most treat it separately).

The striatum :

It consists of two large nuclei:

The caudate nucleus :

The caudate nucleus ^{[32, 66]} is a long, lanky, C-shaped structure that "hugs" the lateral ventricles of the brain. You can visualize its three parts like this:

The Head: The thickest part at the front, which forms the wall of the lateral ventricle.

The Body: The middle section that arches over the thalamus.

The Tail: A thin, tapering end that curves all the way down and forward into the temporal lobe, ending near the amygdala.

The putamen :

The putamen ^{[32, 51]} is a large, rounded structure that forms the outermost layer of the basal ganglia. Its name comes from the Latin word for "nutshell," which describes its hard, protective appearance. Unlike the elongated caudate, the putamen is more lens-shaped (or lentiform).

The pallidum :

Also called the globus pallidus ^{[32, 64]}, it comprises an internal and an external part; together with the putamen, it forms the lenticular nucleus ^{[2, 37, 66]} (so named for its triangular shape on a coronal section).

The subthalamic nucleus :

The subthalamic nucleus ^[64] (body of Luys) is located below the thalamus and above the midbrain. It is a small structure shaped like a biconvex lens.

The substantia nigra :

The substantia nigra ^[38] (locus niger) derives its name from the color of its constituent cells, which are rich in black-colored neuromelanin. It plays a very important role in motor function, producing dopamine (an essential neurotransmitter) in collaboration with other brain structures. Damage to this area is the primary cause of Parkinson's disease ^[79].