Abstract
The subiculum is positioned at a critical juncture at the interface of the hippocampus with the rest of the brain. However, the exact roles of the subiculum in most hippocampal-dependent memory tasks remain largely unknown. One obstacle to make comparisons of neural firing patterns between the subiculum and hippocampus is the broad firing fields of the subicular cells. Here, we used spiking phases in relation to theta rhythm to parse the broad firing field of a subicular neuron into multiple subfields to find the unique functional contribution of the subiculum while male rats performed a hippocampal-dependent visual scene memory task. Some of the broad firing fields of the subicular neurons were successfully divided into multiple subfields similar to those in the CA1 by using the theta phase precession cycle. The new paradigm significantly improved the detection of task-relevant information in subicular cells without affecting the information content represented by CA1 cells. Notably, we found that multiple fields of a single subicular neuron, unlike those in the CA1, carried heterogeneous task-related information such as visual context and choice response. Our findings suggest that the subicular cells integrate multiple task-related factors by using theta rhythm to associate environmental context with action.
Highlights
The hippocampal formation plays key roles in fundamental cognitive functions, including spatial navigation and episodic memory [1,2,3]
We reported that neurons in both the subiculum and CA1 showed rate remapping according to task-related factors, visual scene and choice response in a visual scene memory (VSM) task
Cells recorded from the CA1 fired at focal and restricted locations along the T-maze (Fig 2A), whereas cells recorded from the subiculum tended to show broad and continuous firing fields (Fig 2B), making it challenging to identify a place field using the conventional field detection method based on spatial firing rates
Summary
The hippocampal formation plays key roles in fundamental cognitive functions, including spatial navigation and episodic memory [1,2,3]. The subiculum, a region within the hippocampal formation, has long been considered the area from which cortical outputs of the hippocampus emanate [4,5]. Viewing the subiculum as an area that passively transmits hippocampal information to cortical regions might be inappropriate, because the subiculum is connected with the CA1 of the hippocampus and with other areas, including the medial prefrontal cortex, entorhinal cortex, retrosplenial cortex, perirhinal cortex, postrhinal cortex, nucleus accumbens, basal amygdala, and various subcortical regions [6,7,8].
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