Modulation of task demands suggests that semantic processing interferes with the formation of episodic associations.

Abstract

Although episodic and semantic memory share overlapping neural mechanisms, it remains unclear how our pre-existing semantic associations modulate the formation of new, episodic associations. When freely recalling recently studied words, people rely on both episodic and semantic associations, shown through temporal and semantic clustering of responses. We asked whether orienting participants toward semantic associations interferes with or facilitates the formation of episodic associations. We compared electroencephalographic (EEG) activity recorded during the encoding of subsequently recalled words that were either temporally or semantically clustered. Participants studied words with or without a concurrent semantic orienting task. We identified a neural signature of successful episodic association formation whereby high frequency EEG activity (HFA, 44 – 100 Hz) overlying left prefrontal regions increased for subsequently temporally clustered words, but only for those words studied without a concurrent semantic orienting task. To confirm that this disruption in the formation of episodic associations was driven by increased semantic processing, we measured the neural correlates of subsequent semantic clustering. We found that HFA increased for subsequently semantically clustered words only for lists with a concurrent semantic orienting task. This dissociation suggests that increased semantic processing of studied items interferes with the neural processes that support the formation of novel episodic associations.

Contextually Mediated Spontaneous Retrieval Is Specific to the Hippocampus

“…We predicted that the pattern of activity in hippocampus would be consistent with contextually mediated retrieval, with increased activity for correct recalls only, given the role of hippocampus in contextual encoding [3], source memory [12, 13] and recollection [14, 15]. In comparison, we predicted that our other ROIs would differentiate intrusions and deliberations.…”

“…Based on prior work showing that hippocampal activity correlates with contextual encoding [3], we hypothesized that the hippocampus may also play a unique role in the retrieval of temporal contextual information. It was an open question whether other brain regions within the core memory network would similarly support contextually mediated retrieval.…”

“…Recent intracranial electroencephalographic (iEEG) work has shown that hippocampal activity during encoding predicts subsequent temporal organization of memories [3], supporting a role in contextual binding. It is an open question, however, whether the hippocampus similarly supports contextually mediated processes during retrieval.…”

Neural Pattern Classification Tracks Transfer-Appropriate Processing in Episodic Memory

“…This core prediction of the TAP account has received support from imaging studies (Bauch and Otten, 2012; Fellner et al, 2013; Staudigl and Hanslmayr, 2013; Staudigl et al, 2015; Vogelsang et al, 2016, 2018; Long and Kahana, 2017). Here, we replicate and extend the results from these previous studies by showing that the cortical reinstatement of the encoding brain patterns is only associated with beneficial effects for remembering if the replayed patterns are task relevant.…”

“…Furthermore, previous studies have shown that encoding-related brain activity (i.e., predictive of subsequent memory) is shaped both by the type of processing occurring at encoding and by the overlap between encoding and retrieval processes (Bauch and Otten, 2012; Fellner et al, 2013; Staudigl and Hanslmayr, 2013; Vogelsang et al, 2016; 2018; Long and Kahana, 2017). The typical procedure in these previous studies has been to investigate encoding-related brain activity when explicitly instructing participants to attend to particular attributes during the encoding and retrieval.…”