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Coherence and recurrency: maintenance, control and integration in working memory.

Wolters G, Raffone A - Cogn Process (2007)

Bottom Line: A mechanism that optimizes coherent pattern segregation, also poses a limit to the number of assemblies (about four) that can concurrently reverberate.Hierarchically organized modules in PFC create the possibility for information integration.We argue that large-scale multimodal integration of information creates an 'episodic buffer', and may even suffice for implementing a central executive.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychology, Institute for Psychological Research, Leiden University, Leiden, The Netherlands. wolters@fsw.leidenuniv.nl

ABSTRACT
Working memory (WM), including a 'central executive', is used to guide behavior by internal goals or intentions. We suggest that WM is best described as a set of three interdependent functions which are implemented in the prefrontal cortex (PFC). These functions are maintenance, control of attention and integration. A model for the maintenance function is presented, and we will argue that this model can be extended to incorporate the other functions as well. Maintenance is the capacity to briefly maintain information in the absence of corresponding input, and even in the face of distracting information. We will argue that maintenance is based on recurrent loops between PFC and posterior parts of the brain, and probably within PFC as well. In these loops information can be held temporarily in an active form. We show that a model based on these structural ideas is capable of maintaining a limited number of neural patterns. Not the size, but the coherence of patterns (i.e., a chunking principle based on synchronous firing of interconnected cell assemblies) determines the maintenance capacity. A mechanism that optimizes coherent pattern segregation, also poses a limit to the number of assemblies (about four) that can concurrently reverberate. Top-down attentional control (in perception, action and memory retrieval) can be modelled by the modulation and re-entry of top-down information to posterior parts of the brain. Hierarchically organized modules in PFC create the possibility for information integration. We argue that large-scale multimodal integration of information creates an 'episodic buffer', and may even suffice for implementing a central executive.

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Scheme of the cortical network architecture. In the IT module, 20 neural assemblies code for 20 hypothetical visual features or separate representational elements. The figure shows the case with five four-feature chunks, with synchronizing connections between the assemblies coding the features of the same object (depicted as diamond-like configurations). The IT module also comprises an assembly of globally inhibitory neurons, which are implicitly modeled through inhibitory postsynaptic potentials (IPSPs). The vlPFC module is a set of 20 assemblies of neurons, with a coding structure “matching” the IT module structure. For simplicity, each IT assembly is recurrently connected with one vlPFC assembly, with a signaling delay of 15 ms in both directions. The vlPFC assemblies coding for a given chunk are reciprocally connected with a dlPFC assembly, which propagates synchronous firing before Hebbian learning takes place in the IT module
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Fig2: Scheme of the cortical network architecture. In the IT module, 20 neural assemblies code for 20 hypothetical visual features or separate representational elements. The figure shows the case with five four-feature chunks, with synchronizing connections between the assemblies coding the features of the same object (depicted as diamond-like configurations). The IT module also comprises an assembly of globally inhibitory neurons, which are implicitly modeled through inhibitory postsynaptic potentials (IPSPs). The vlPFC module is a set of 20 assemblies of neurons, with a coding structure “matching” the IT module structure. For simplicity, each IT assembly is recurrently connected with one vlPFC assembly, with a signaling delay of 15 ms in both directions. The vlPFC assemblies coding for a given chunk are reciprocally connected with a dlPFC assembly, which propagates synchronous firing before Hebbian learning takes place in the IT module

Mentions: Here, we will explore an extension of the model of Raffone and Wolters (2001), simulating not only maintenance, but also a selective attention mechanism and a particular characteristic of an integration mechanism. The network architecture presented here to model these functions, is composed of three modules, which we assume to correspond to an IT module, a ventrolateral prefrontal module (vlPFC), and a dorsolateral prefrontal module (dlPFC), respectively (see Fig. 2). We assume that visual features are coded by individual assemblies of neurons in IT, which are “matched” to one assembly in vlPFC in a recurrent circuit. Moreover, we assume that different subsets of four vlPFC assemblies coding for given visual chunks, are bi-directionally connected to dlPFC assemblies (one for each set of four vlPFC assemblies).Fig. 2


Coherence and recurrency: maintenance, control and integration in working memory.

Wolters G, Raffone A - Cogn Process (2007)

Scheme of the cortical network architecture. In the IT module, 20 neural assemblies code for 20 hypothetical visual features or separate representational elements. The figure shows the case with five four-feature chunks, with synchronizing connections between the assemblies coding the features of the same object (depicted as diamond-like configurations). The IT module also comprises an assembly of globally inhibitory neurons, which are implicitly modeled through inhibitory postsynaptic potentials (IPSPs). The vlPFC module is a set of 20 assemblies of neurons, with a coding structure “matching” the IT module structure. For simplicity, each IT assembly is recurrently connected with one vlPFC assembly, with a signaling delay of 15 ms in both directions. The vlPFC assemblies coding for a given chunk are reciprocally connected with a dlPFC assembly, which propagates synchronous firing before Hebbian learning takes place in the IT module
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2254470&req=5

Fig2: Scheme of the cortical network architecture. In the IT module, 20 neural assemblies code for 20 hypothetical visual features or separate representational elements. The figure shows the case with five four-feature chunks, with synchronizing connections between the assemblies coding the features of the same object (depicted as diamond-like configurations). The IT module also comprises an assembly of globally inhibitory neurons, which are implicitly modeled through inhibitory postsynaptic potentials (IPSPs). The vlPFC module is a set of 20 assemblies of neurons, with a coding structure “matching” the IT module structure. For simplicity, each IT assembly is recurrently connected with one vlPFC assembly, with a signaling delay of 15 ms in both directions. The vlPFC assemblies coding for a given chunk are reciprocally connected with a dlPFC assembly, which propagates synchronous firing before Hebbian learning takes place in the IT module
Mentions: Here, we will explore an extension of the model of Raffone and Wolters (2001), simulating not only maintenance, but also a selective attention mechanism and a particular characteristic of an integration mechanism. The network architecture presented here to model these functions, is composed of three modules, which we assume to correspond to an IT module, a ventrolateral prefrontal module (vlPFC), and a dorsolateral prefrontal module (dlPFC), respectively (see Fig. 2). We assume that visual features are coded by individual assemblies of neurons in IT, which are “matched” to one assembly in vlPFC in a recurrent circuit. Moreover, we assume that different subsets of four vlPFC assemblies coding for given visual chunks, are bi-directionally connected to dlPFC assemblies (one for each set of four vlPFC assemblies).Fig. 2

Bottom Line: A mechanism that optimizes coherent pattern segregation, also poses a limit to the number of assemblies (about four) that can concurrently reverberate.Hierarchically organized modules in PFC create the possibility for information integration.We argue that large-scale multimodal integration of information creates an 'episodic buffer', and may even suffice for implementing a central executive.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychology, Institute for Psychological Research, Leiden University, Leiden, The Netherlands. wolters@fsw.leidenuniv.nl

ABSTRACT
Working memory (WM), including a 'central executive', is used to guide behavior by internal goals or intentions. We suggest that WM is best described as a set of three interdependent functions which are implemented in the prefrontal cortex (PFC). These functions are maintenance, control of attention and integration. A model for the maintenance function is presented, and we will argue that this model can be extended to incorporate the other functions as well. Maintenance is the capacity to briefly maintain information in the absence of corresponding input, and even in the face of distracting information. We will argue that maintenance is based on recurrent loops between PFC and posterior parts of the brain, and probably within PFC as well. In these loops information can be held temporarily in an active form. We show that a model based on these structural ideas is capable of maintaining a limited number of neural patterns. Not the size, but the coherence of patterns (i.e., a chunking principle based on synchronous firing of interconnected cell assemblies) determines the maintenance capacity. A mechanism that optimizes coherent pattern segregation, also poses a limit to the number of assemblies (about four) that can concurrently reverberate. Top-down attentional control (in perception, action and memory retrieval) can be modelled by the modulation and re-entry of top-down information to posterior parts of the brain. Hierarchically organized modules in PFC create the possibility for information integration. We argue that large-scale multimodal integration of information creates an 'episodic buffer', and may even suffice for implementing a central executive.

Show MeSH
Related in: MedlinePlus