Time-locked multiregional retroactivation: A systems-level proposal for the neural substrates of recall and recognition

Abstract

This article outlines a theoretical framework for the understanding of the neural basis of memory and consciousness, at systems level. It proposes an architecture constituted by: (1) neuron ensembles located in multiple and separate regions of primary and first-order sensory association cortices ("early cortices") and motor cortices; they contain representations of feature fragments inscribed as patterns of activity originally engaged by perceptuomotor interactions; (2) neuron ensembles located downstream from the former throughout single modality cortices (local convergence zones); they inscribe amodal records of the combinatorial arrangement of feature fragments that occurred synchronously during the experience of entities or events in sector (1); (3) neuron ensembles located downstream from the former throughout higher-order association cortices (non-local convergence zones), which inscribe amodal records of the synchronous combinatorial arrangements of local convergence zones during the experience of entities and events in sector (1); (4) feed-forward and feedback projections interlocking reciprocally the neuron ensembles in (1) with those in (2) according to a many-to-one (feed-forward) and one-to-many (feedback) principle. I propose that (a) recall of entities and events occurs when the neuron ensembles in (1) are activated in time-locked fashion; (b) the synchronous activations are directed from convergence zones in (2) and (3); and (c) the process of reactivation is triggered from firing in convergence zones and mediated by feedback projections. This proposal rejects a single anatomical site for the integration of memory and motor processes and a single store for the meaning of entities of events. Meaning is reached by time-locked multiregional retroactivation of widespread fragment records. Only the latter records can become contents of consciousness.

Neural systems underlying lexical retrieval for sign language

“…These cortical regions lie outside the classical language areas and are hypothesized to contain neuron ensembles that can transiently direct the reconstruction of phonological representation (e.g. [11,12]). These results suggest that the modality of the phonological representation (auditory-oral or visual-manual) does not substantially alter the neural substrate for lexical mediation between concepts and the production of lexical items.…”

A role for left temporal pole in the retrieval of words for unique entities

“…Because the processes underlying concept retrieval and language implementation are supported by different neural systems, the process of word retrieval implies coordination of activity among separate neural regions. We interpret the role of the left TP in the context of a theoretical framework [Damasio, 1989;Damasio and Damasio, 1994;Tranel et al, 1997aTranel et al, , 1997b in which wordform production is dependent on three kinds of neural structures: (1) those structures which support conceptual knowledge (in early and high-order sensory cortices of both hemispheres); (2) those structures which support the implementation of word-forms in vocalization (in classical left perisylvian language areas); and (3) mediational structures, such as left TP, which are engaged by the structures in (1) to guide the implementation process executed in (2). The sensorimotor patterns on the basis of which word-forms are explicitly represented in mind are triggered by relevant mediational circuits and occur in early sensory cortices (e.g., auditory) and motor structures.…”

Hemispheric Independence in Word Recognition: Evidence from Unilateral and Bilateral Presentations

“…We posit that each hemisphere has a different lexical semantic system that encompasses sets of neural cell assemblies which are represented throughout association cortex and correspond to semantic fea-tures. Word recognition involves synchronous activation of those multiple representations, coordinated, paced, and controlled by ''convergence zones'' (lexical entries) (Damasio, 1989;Damasio & Damasio, 1990), and semantic features from both hemispheres may converge to facilitate processing. This implies that bilateral copies of the word should be more potent in generating resource sharing than either single unilateral copies or two copies in the same hemisphere (Mohr, Pulvermuller, & Zaidel, 1994;Zaidel & Rayman, 1994a).…”