TABLE 2.

Overview of subcompartment-specific cell-nucleus expression of immediate early genes triggered by either different kinds of spatial learning or by task-specific facilitation of hippocampal LTP or LTD.

Synaptic plasticity facilitated by new spatial exploration or induced by stimulation	dCA1	pCA1	dCA3	pCA3	uDG	lDG
LTP, empty holeboard	↑H1a2	↑H1a2	↑H1a2	↑H1a2	↑H1a2	↑H1a2
LTD, small objects	↑Arc1	– Arc1	– Arc1	↑Arc1	– Arc1	– Arc1
	↑ c-Fos4*
LTD, landmarks	– Arc1, H1a2	– Arc1, H1a2	–H1a1,2	↑H1a1,2	–Arc1, H1a1,2	↑Arc1, H1a1,2
LTP induced by HFS	↑ H1a2	↑ H1a2	↑ H1a2	↑ H1a2	↑ H1a2	↑ H1a2
	↑ Arc3**
LTD induced by LFS	↑ H1a2	↑ H1a2	↑ H1a2	↑ H1a2	↑ H1a2	↑ H1a2
	↓↑Arc3**

*The expression of c-Fos was analyzed in the whole hippocampus without subdifferentiation.

**Arc expression was analyzed only in the dorsal CA1, without differentiation between proximal and distal subdivisions.

The abbreviations correspond to the dorsal CA1 (dCA1), proximal CA1 (pCA1), dorsal CA3 (dCA3), proximal CA3 (pCA3), the upper (suprapyramidal) blade of the DG (uDG), and the lower (infrapyramidal) blade of the DG (lDG).

An arrow indicates that a significant increase in IEG expression [cFos, Arc or Homer1a (H1a)] was triggered by the event.

A dash signifies that no change occurred compared to naïve controls.

What is striking is that LTP that is facilitated by de novo exposure to unfamiliar space results in IEG expression in neuronal populations across all hippocampal subfields and subcompartments.

By contrast, LTD that is facilitated by learning results in an expression-pattern that is tightly dependent upon the kind of spatial content learning conducted.

The data summarized in the table were reported in ¹Hoang et al. (2018), ²Hoang et al. (2021), ³Yilmaz-Rastoder et al. (2011), and ⁴Kemp et al. (2013).