Recurrent Neural Processing and Somatosensory Awareness

Abstract

The neural mechanisms of stimulus detection, despite extensive research, remain elusive. The recurrent processing hypothesis, a prominent theoretical account of perceptual awareness, states that, although stimuli might in principle evoke feedforward activity propagating through the visual cortex, stimuli that become consciously detected are further processed in feedforward-feedback loops established between cortical areas. To test this theory in the tactile modality, we applied dynamic causal modeling to electroencephalography (EEG) data acquired from humans in a somatosensory detection task. In the analysis of stimulation-induced event-related potentials (ERPs), we focused on model-based evidence for feedforward, feedback, and recurrent processing between primary and secondary somatosensory cortices. Bayesian model comparison revealed that, although early EEG components were well explained by both the feedforward and the recurrent models, the recurrent model outperformed the other models when later EEG segments were analyzed. Within the recurrent model, stimulus detection was characterized by a relatively early strength increase of the feedforward connection from primary to secondary somatosensory cortex (Ͼ80 ms). At longer latencies (Ͼ140 ms), also the feedback connection showed a detection-related strength increase. The modeling results on relative evidence between recurrent and feedforward model comparison support the hypothesis that the ERP responses from sensory areas arising after aware stimulus detection can be explained by increased recurrent processing within the somatosensory network in the later stages of stimulus processing.

Oscillatory activity in neocortical networks during tactile discrimination near the limit of spatial acuity

“…Accuracy of tactile discrimination was significantly correlated with measures of network activity in both bands. These results provide direct evidence of recurrent information processing of sensory and attentional signals as in somatosensory awareness (Auksztulewicz et al, 2012) and in other forms of decision-making (Klein-Flugge and Bestmann, 2012; Selen et al, 2012). These findings, together with previous studies in the visual (Siegel et al, 2011) and auditory-visual domains (Hipp et al, 2011) suggest common oscillatory network mechanisms for perceptual decision-making across various sensory modalities.…”

Cortical activity is more stable when sensory stimuli are consciously perceived

“…Dynamic long-range phase synchrony is also enhanced when visual stimuli are consciously seen (14,22,50). Importantly, recurrent rather than feed-forward interactions have been implicated in conscious perception (8,51), and such interactions may reflect a process of convergence toward a transiently stable state (9). The notion of transient stability (or metastability) has been invoked in many theoretical accounts of conscious sensory perception (9,11,13,15,37,52,53).…”

Evidence for embodied predictive coding: the anterior insula coordinates cortical processing of tactile deviancy

“…Indeed, recurrent neural activity in the somatosensory hierarchy has previously been shown to be important for conscious somatosensory awareness (Auksztulewicz et al 2012); in general such cortical-subcortical loops are thought to be critical for conscious awareness (Dehaene et al 2014). Here we found that strong recurrent connectivity between the AIC and somatosensory cortex supports the processing of tactile oddballs, and that individual differences in the strength of backwards influences from the PFC to AIC predicted the self-rated ease of detecting subtle stimulus changes.…”

“…Somatosensation underlies the conscious body-image that underpins body-ownership and action agency (Serino and Haggard 2010) and has recently been shown to rely on hierarchical Bayesian inferences (Auksztulewicz et al 2012;Ostwald et al 2012). The AIC is richly interconnected with the posterior insula and somatosensory cortex (Cerliani et al 2012;Chang et al 2012), and anticipates the sensory and affective consequences of touch (Lovero et al 2009).…”