Jonathan Najenson

This chapter examines the relationship between cognitive maps and episodic memory, and the tensions that arise when we aim to integrate these capacities. I trace the evolution of cognitive maps from Tolman's behavioral studies through the discoveries of place cells, head direction cells, and grid cells, examining how understanding cognitive maps was guided by the type of computations required for physical navigation. I then review how philosophers have sought to explain cognitive maps and spatial representations as computational structures required to encode and retrieve information about the past. However, I show that despite shared neural architecture in the hippocampal formation, mechanistic decomposition reveals tensions between cognitive maps and episodic memory: either episodic memory requires mechanistic components beyond traditional memory circuits, or cognitive maps contribute only partially to memory function. This suggests we must either recharacterize episodic memory or limit cognitive maps' explanatory use for understanding episodic memory.

The identification of memory engrams remains a methodological obstacle in neuroscience if they are to play the explanatory role ascribed to them by engram theory. I tackle the problem of specificity, namely the extent to which engrams can be identified, tracked, and distinguished from other engram and non-engram vehicles. I propose that adopting causal specificity from the interventionist framework of causation allows us to describe how engrams are specific to the memories and behaviors they generate. Drawing on recent work using information-theoretic measures to describe causal specificity, I illustrate how this approach can be used to model the reduction of uncertainty about retrieved memories following optogenetic interventions on engram cells.

The origin of memories is thought to be found in sensory perception. This conception is central to how the memory sciences characterize encoding. This paper considers how novel memory traces can be formed independently of external sensory inputs. I present a case study in which memory traces are created without sensory perception using a technique I call optogenetic memory implantation. Comparing this artificial process with normal memory encoding, I consider its implications for rethinking the causal chain that leads to remembering.

Changes in synaptic strength are described as a unifying hypothesis for memory formation and storage, leading philosophers to consider the ‘synaptic efficacy hypothesis’ as a paradigmatic explanation in neuroscience. Craver’s mosaic view has been influential in understanding synaptic efficacy by presenting long-term potentiation as a multi-level mechanism nested within a multi-level structure. This paper argues that the mosaic view fails to fully capture the explanatory power of the synaptic efficacy hypothesis due to assumptions about multi-level mechanisms. I present an alternative approach that emphasizes the explanatory function of unification, accounting for the widespread consensus in neuroscience regarding synaptic efficacy by highlighting the stability of synaptic causal variables across different multi-level mechanisms.

The discovery of the engram, the physical substrate of memory, is a central challenge for the sciences of memory. Following the application of optogenetics to the neurobiological study of memory, scientists and philosophers claim that the engram has been found. In this paper, I evaluate the implications of applying optogenetic tools to the localization of the engram. I argue that conceptions of engram localization need to be revised to be made consistent with optogenetic studies of the engram. I distinguish between challenges to vehicle and content localization. First, I consider the silent engram hypothesis. According to this hypothesis, optogenetic studies indicate that synaptic efficacy, the traditional engram-bearing vehicle, is important merely for retrieval. I argue that this interpretation rests upon a misunderstanding of accessibility. Second, I argue that optogenetic-based strategies and findings conflict with preservationist and constructivist views on memory storage. There is an enduring trace, but stored content may change over time and experience, resulting in doubt about what constitutes a single engram.

According to a standard view in psychology and neuroscience, there are multiple memory systems in the brain. Philosophers and scientists of memory rely on the idea that there are multiple memory systems in the brain to infer that procedural memory is not a cognitive form of memory. As a result, memory is considered to be a disunified capacity. In this article, I evaluate two criteria used by Michaelian to demarcate between cognitive and non-cognitive memory systems: appeal to stored content and retrieval flexibility. By considering several empirical cases I argue that the criteria offered ultimately fail to distinguish between memory systems. The procedural memory system is neither contentless nor inflexible.