The habenula is a tiny paired structure deep in the centre of the brain, in the epithalamus at the top back of the thalamus, where it borders the third ventricle just in front of the pineal gland. It links the forebrain to the midbrain. [1]
The model draws the left and right habenulae and the habenular commissure that joins them as one small shape across the midline, so they are lit together as one part and not side by side. [2][1]
The 3D brain needs JavaScript. The text below still says where the habenula is and what it does.
Slice
Opens cut by a side (sagittal) slice through the habenula. Drag to turn, pinch or scroll to zoom, tap any part to name it; .
In the epithalamus, the back (dorsal) part of the diencephalon, where it borders the third ventricle and lies in front of the pineal gland. [1][3]
One on each side; the right and left habenular nuclei are joined by the habenular commissure, and the pineal gland is attached to the brain in this region. [1]
With the stria medullaris, a ridge of white matter along the top inner edge of the thalamus, and the habenular commissure, it forms the habenular trigone. [4]
What it does
It connects forebrain regions to midbrain regions and acts as a hub for combining emotional and sensory information, taking in signals from the limbic system, sensory areas and the basal ganglia. [1]
Its lateral part is “reward-negative”: its neurons fire for unpleasant events and when an expected reward does not come, especially when that is unpredictable, and in turn they hold back the dopamine neurons of the substantia nigra and ventral tegmental area. [1]
It helps regulate the brain’s dopamine and serotonin centres, and takes part in motivation, emotion, learning, pain, stress responses and sleep–wake cycles. [1]
The lateral habenula plays a part in learning to avoid things (acquiring avoidance responses) and may play a role in decision making. [1]
Connections
In: the stria medullaris is its main input bundle, bringing fibres from the septal nuclei, the lateral preoptic and hypothalamic region and the anterior thalamic nuclei. [4]
The lateral habenula also receives input from the lateral hypothalamus, nucleus accumbens, internal globus pallidus and ventral pallidum. [1]
Out: the lateral habenula projects to dopamine areas (substantia nigra pars compacta, ventral tegmental area) and serotonin areas (median and dorsal raphe nuclei); the medial habenula sends fibres through the interpeduncular nucleus to the periaqueductal grey, a route called the fasciculus retroflexus. [1]
Inside it
Each side has two divisions with different cells, inputs and outputs: a medial habenula (five subnuclei) and a lateral habenula (four subnuclei). [1]
Other names
Habenular nuclei (habenular nucleus for one side); plural habenulae. The name is the diminutive of Latin habena, “rein”, so “little rein”, for its long shape. [1]
On this model the habenula measures about 5 mm front to back, 4 mm top to bottom and 8 mm side to side (the box it fits in, not its volume). [2]
Centre of the habenula compared with the centre of the pineal gland: 5 mm further forward; 6 mm apart in a straight line. [2]
Centre of the habenula compared with the centre of the left thalamus: 9 mm further back, 7 mm lower, 13 mm closer to the midline; 17 mm apart in a straight line. [2]
Facts describe anatomy and normal function only. The 3D model is the adult male BodyParts3D brain (credits and licence); real brains vary in size and shape, so its measurements describe one model, not anyone’s brain.