Hypothalamus and Limbic System Functions
Tuberal Region of the Hypothalamus
Dorsomedial Nucleus
When stimulated in animals, the Dorsomedial Nucleus produces aggressive behavior.
Ventromedial Nucleus
- Considered the satiety center.
- When stimulated, it inhibits the need to eat.
- Bilateral destruction results in hyperphagia, obesity, and aggressive behavior.
Mammillary Region
Mammillary Nucleus
- Receives input from the parahippocampal formation (subiculum) through the fornix.
- Projects to the anterior thalamic tract through the mammillothalamic tract.
- Associated with Wernicke encephalopathy.
Lateral Nucleus
- Plays a role in thermoregulation (maintaining and increasing heat production).
- Injury to this area results in poikilothermia (the loss of thermoregulation).
Hypothalamic Connections
Afferent Connections
- Septal nuclei
- Hippocampus
- Amygdaloid complex
- Primary olfactory cortex (Area 34)
- Mediodorsal thalamus
- Nuclei from the brainstem (tegmental, raphe, and locus coeruleus)
Efferent Connections
- Septal nuclei
- Anterior thalamus
- Mediodorsal thalamus
- Amygdaloid complex
- Nuclei from the brainstem
- Adenohypophysis and neurohypophysis
Autonomic Function Regulation
Autonomic function is regulated by specific hypothalamic nuclei:
- Anterior Hypothalamus: Has an excitatory effect on the parasympathetic Autonomic Nervous System (ANS).
- Posterior Hypothalamus: Has an excitatory effect on the sympathetic Autonomic Nervous System (ANS).
Efferents of the Amygdala
Information travels from the amygdala through two main channels:
- The stria terminalis
- The ventral amygdalofugal pathway
Behavioral and Emotional Functions
Affective Aggression
This is usually directed at members of the same species and aims to defend rights regarding food, territory, or mating.
Effects Caused by Stimulation
Apart from the vegetative functions of the hypothalamus, stimulation or lesions often exert profound effects on emotional behavior:
- Lateral Hypothalamus: Stimulation causes not only thirst and eating, but also anger or fighting.
- Ventromedial Nucleus: Stimulation of this nucleus and adjacent structures often causes a feeling of satiety, decreased food intake, and tranquility.
- Periventricular Zone: Stimulation of these thin nuclei usually results in reactions of fear and punishment.
- Sex Drive: Regulated by areas of the hypothalamus, especially in its most anterior and most posterior regions.
Hippocampal Formation
The hippocampal formation consists of three parts:
- The dentate gyrus
- The hippocampus
- The subiculum
Role of the Hippocampal Formation
- It builds memories and establishes relationships between them.
- Hippocampal lesions can alter this system, preventing the formation of new memories while retaining old ones (anterograde amnesia).