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. 2022 Apr 25;16:806356. doi: 10.3389/fnbeh.2022.806356

FIGURE 3.

FIGURE 3

Hypothetical schema of the proposed role for LTD in enabling discriminable spatial representations. Top: The upper photo (Event A, left) is of a landscape near Damariscotta in Maine, United States. By means of LTP the general schema of this landscape is presumably obtained (large dark blue dots, right) (Kemp and Manahan-Vaughan, 2007; Manahan-Vaughan, 2017). Content details are retained by means of LTD (Kemp and Manahan-Vaughan, 2008a; Manahan-Vaughan, 2017) that serves to eliminate weakly potentiated synapses (green dots), or weaken communications between synapses. By this means a robust representation is obtained. Middle: The photo (left) is of Hook Head in Ireland (Event B). When we acquire new memories we are very likely to use blueprints of past memories of similar experiences. Thus, elements of a previously stored neuronal and synaptic network can be re-used as a framework for, in this case, the promontory-like features of the scene, the water inlets and the general global composition of the landscape encoded in Event A. LTD serves to remove superfluous elements, of the new representation compared to the Maine landscape (the asphalt element in the foreground, the trees lining the horizon). De novo LTP is likely to support the retention of new general features of the landscape (large purple dots, right) (Kemp and Manahan-Vaughan, 2004; Manahan-Vaughan, 2018a) and LTD contributes to information encoding through the inclusion of content details such as the houses and the lighthouse (Kemp and Manahan-Vaughan, 2008a; Manahan-Vaughan, 2017, 2018a). Where LTP and LTD work together, LTD serves to modify the new network, thereby enabling pattern separation (Manahan-Vaughan, 2018a; Collitti-Klausnitzer et al., 2021). Bottom left: In the absence of the refinement of signal-to-noise ratios and suppression of redundant synaptic connections, in the new representation by means of LTD, the former potentiated network merges with the new network and the memory of both experiences becomes generalized into one representation (bottom right). Photos: D. Manahan-Vaughan.