Binding binding: Departure points for a different version of the perceptual retouch theory

Abstract

In the perceptual retouch theory, masking and related microgenetic phenomena were explained as a result of interaction between specific cortical representational systems and the non-specific sub-cortical modulation system. Masking appears as deprivation of sufficient modulation of the consciousness mechanism suffered by the target-specific signals because of the temporal delay of non-specific modulation (necessary for conscious representation), which explicates the later-coming mask information instead of the already decayed target information. The core of the model envisaged relative magnitudes of EPSPs of single cortical cells driven by target and mask signals at the moment when the nonspecific, presynaptic, excitatory input arrives from the thalamus. In the light of the current evidence about the importance of synchronised activity of specific and non-specific systems in generating consciousness, the retouch theory requires perhaps a different view. This article presents some premises for modification of the retouch theory, where instead of the cumulative presynaptic spike activities and EPSPs of single cells, the oscillatory activity in the gamma range of the participating systems is considered and shown to be consistent with the basic ideas of the retouch theory. In this conceptualisation, O-binding refers to specific encoding which is based on gamma-band synchronised oscillations in the activity of specific cortical sensory modules that represent features and objects; C-binding refers to the gamma-band oscillations in the activity of the non-specific thalamic systems, which is necessary for the O-binding based data to become consciously experienced.

Keywords: consciousness; gamma-oscillations; masking; perceptual retouch; synchronization; thalamic modulation.

Figure 1.

A schematic of the functional architecture of the two interacting systems for sensory data processing. Specific pathways (SP) send sensory signals upstream to the specific cortical modules that encode stimuli features and integrate objects in terms of their specific contents. This fast system builds perceptual representations also pre-consciously. A slower, non-specific system (NSP), which is located in feature-wise non-specialised thalamic and reticular centers (e.g., intralaminar nuclei, reticular nucleus, globus pallidum), interacts with cortical specific units by modulating cortical activity, preferrably in a facilitative way, increasing the frequency of firing of the specific units, decreasing their firing latency and modulating the timing of discharge patterns. The SP-system serves for binding objects from features (O-binding), the NSP system serves for modulating the activities of the O-binding system up to the level which is sufficient for explicit perception (consciousness) of the perceptual representations carried by the specific representational units. O-binding system work is necessary for the contents of conscious perception, but insufficient without the additional upgrading by the C-binding system. Both systems together are sufficient for perceptual consciousness.

Figure 2.

A schematic of a cortical slice where interaction between O-binding (left-side loop) and C-binding (right-side loop) systems takes place at the single-unit level. (The central part of this picture is adapted from Llinas, R.R., Urbano, F.J., Leznik, E., Ramirez, R.R., & van Marle, H.J.F. (2005). Rhythmic and dysrhythmic thalamocortical dynamics: GABA systems and the edge effect. TINS, 28(6), 325-333.) The specific pathway activates pyramidal neurons and inhibitory interneurons (upper red), producing cortical oscillations by direct activation and feedforward inhibition. Collaterals from this pathway produce thalamic feedback inhibition through the reticular nucleus (lower red). The return corticothalamic pathway (curved green arrow) from pyramidal cells returns this oscillatory loop to specific and reticular thalamic nuclei (yellow and red lower circles). The non-specific thalamocortical pathway projects to the cortex and gives collaterals to the reticular nucleus. Pyramidal neurons return the oscillation to the non-specific and reticular thalamic nuclei (green and red lower circles). This forms the second resonant loop (curved green arrow on the right). The conjunction of the specific and non-specific loops is hypothesised to generate functional binding by temporal coincidence.

Figure 3.

An illustration of the functional relationship relating SOA (set between prime and target) with perceptual asynchrony between targets presented in control conditions without prime and main experimental conditions where prime precedes target. The slope of the function is about 0.5. (Adapted from Aschersleben and Bachmann, 2004, unpublished.)