Single neurons in the human medial temporal lobe flexibly shift representations across spatial and memory tasks

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Systems Neuroscience

Background:

• Single neurons exhibit diverse encoding strategies, including specific (place, object) and mixed selectivity.
• Neural representations across different task contexts remain poorly understood, particularly in the medial temporal lobe (MTL).
• The MTL is crucial for spatial navigation and memory, but the interplay between these functions at the neural level is unclear.

Purpose of the Study:

• To investigate how single-neuron representations in the human MTL vary across distinct task contexts.
• To determine if neural representations are stable or flexible when switching between visual working memory and spatial navigation tasks.

Main Methods:

• Recorded single-neuron activity from five human patients performing paired visual working memory and spatial navigation/memory tasks.
• Utilized spike sorting to compare activity from the same putative neurons across both tasks.
• Analyzed neural responses for concept-related activations (working memory) and target-location/serial-position coding (navigation).

Main Results:

• Confirmed known neural representations within each task (concept-specific in working memory, location/serial-position in navigation).
• A significant proportion of neurons maintained consistent representations across tasks.
• Identified neurons that altered their representational code, notably stimulus-responsive cells in working memory becoming serial-position responsive in navigation.

Conclusions:

• Single neurons in the human MTL demonstrate flexible encoding capabilities, representing distinct features of different tasks.
• Some individual neurons dynamically shift their feature coding depending on the cognitive context.
• These findings support a model of adaptable neural representations supporting multiple cognitive functions within the MTL.