1. Neuroanatomy and limbic system functions 

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Steve Lampa
PhD · Clinical Associate Professor
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Functions regulated by the limbic system

Mnemonic

Use the acronym HOME.

Homeostasis: Maintains internal physiological balance via hypothalamic connections.

Olfaction: Processes smell through olfactory pathways.

Memory: Especially episodic and spatial memory via the medial temporal lobe.

Emotion: Modulates emotional responses through the Papez circuit and amygdala.

Medial temporal lobe: Central to memory

  • Includes the hippocampus, amygdala, and parahippocampal gyrus.

  • Supports encoding, consolidation, and retrieval of memory.

  • The hippocampal formation (dentate gyrus, hippocampus, subiculum) is key for explicit and spatial memory.

Hippocampus from Radiopaedia.

Amygdala: Integrates sensory input for emotional responses

  • Receives diverse sensory input (olfactory, visual, auditory, etc.).

  • Sends output to the hypothalamus and brainstem, influencing autonomic and defensive behaviors.

  • Plays a major role in fear, anxiety, and emotional memory.

Coronal image showing the location of the amygdala. From Nolte’s The Human Brain.

Limbic axonal pathways: Connect emotion and cognition

  • Fornix

    A major white matter tract linking the hippocampus to the hypothalamus and basal forebrain.

  • Mammillothalamic tract

    Connects mammillary bodies to the anterior thalamus, which projects to the cingulate gyrus.

  • Axonal pathways

    These axonal pathways integrate memory, emotion, and autonomic responses and are central to Papez circuit.

The Papez circuit

In 1937 James Papez described a neural circuit for the cortical control of emotions. Since then the circuit has been extensively studied and is now believed to be the major pathway for storing memory. It shows that neural pathways connect the hippocampus with the limbic system, indicating that memories that are stored from the hippocampus have a heavy emotional content. This may partly explain why we tend to remember happy or sad moments of life more readily than ‘routine’ everyday events. This circuit also explains why some memories also tend to cause autonomic effects; for example, the very memory of the sour taste of lemon may cause us to salivate.

 

Briefly, the circuit starts with the hippocampus connecting to mammillary bodies (part of the thalamus), through the subiculum and fornix. The mammillary bodies send signals to anterior thalamic nuclei, from there to the cingulate gyrus. The cingulate gyrus sends back signals to the limbic system and to the cortex (to show overt body effects and feelings).

Source: AI-generated definition based onTextbook of Clinical Neurology, 3e, 2007.

Basal forebrain and VTA: Modulate limbic system activity

  • Basal forebrain

    Contains cholinergic neurons (e.g., nucleus basalis of Meynert) projecting to the neocortex and hippocampus; vulnerable in Alzheimer’s disease.

  • Ventral tegmental area (VTA) of the midbrain

    Sends dopaminergic projections to limbic and cortical areas, influencing motivation, reward, and emotion.

Review questions

Review

Which structure is primarily involved in encoding and retrieving explicit and spatial memory?

Case study

César, a patient with Alzheimer's disease, shows significant degeneration in the basal forebrain. Which of the following symptoms is most likely explained by this pathology?

The basal forebrain, particularly the nucleus basalis of Meynert, contains cholinergic neurons that project to the neocortex and hippocampus. Their degeneration is linked to cognitive decline in Alzheimer’s.

Review

Damage to the mammillothalamic tract would most directly impair which of the following neural processes?

The mammillothalamic tract connects the mammillary bodies to the anterior thalamus, which is part of the Papez circuit—a key pathway for memory and emotional integration.

Review

A researcher is studying the interaction between emotional memory and autonomic responses. Which combination of limbic structures and pathways would be most relevant to investigate?

  • The amygdala integrates sensory input for emotional responses and influences autonomic behavior via its connections to the hypothalamus and brainstem.
  • The fornix links the hippocampus to limbic structures, facilitating emotional memory and autonomic integration.

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Image credits

Unless otherwise noted, images are from Adobe Stock.