Brain stimulation and conscious experience: electrical stimulation of the cortical surface at a threshold current evokes sustained neuronal activity only after a prolonged latency

Libet demonstrated that a substantial duration (>0.5-1.0 s) of direct electrical stimulation of the surface of a sensory cortex at a threshold or liminal current is required before a subject can experience a percept. Libet and his co-workers originally proposed that the result could be due either to spatial and temporal facilitation of the underlying neurons or additionally to a prolonged central processing time. However, over the next four decades, Libet chose to attribute the prolonged latency for evoking conscious experience to a prolonged central processing time. In my view, Libet has not provided any convincing evidence, either on the basis of his own past work or in his critique of my paper, for his hypothesis of a central processing time exceeding 0.5s before conscious experience emerges following direct electrical threshold stimulation of the cortical surface. I stand by my original results and conclusion that such prolonged latencies are largely the consequence of a dynamically increasing cortical facilitatory process that begins hundreds of milliseconds before there is a sustained neuronal activation. In some cases, the facilitatory process must overcome an initial stimulus-induced inhibition before neuronal firing commences.     

From conscious experience to a conscious self

In his book The Opacity of Mind, Peter Carruthers (2011 Carruthers, P. (2011). The opacity of mind: An integrative theory of self-knowledge. Oxford: Oxford University Press.[Crossref] , [Google Scholar]) presents the Interpretive Sensory Awareness theory (“ISA”), which holds that while we have direct access to our own sensory states, our access to “self-knowledge” is almost always interpretive. In presenting his view, Carruthers also claims that his account is the first of its kind; after a cursory examination of major theories of mind, he concludes that “transparent access” accounts of self-knowledge—the alternative to ISA—have been endorsed throughout history. This paper challenges this latter claim. Contrary to Carruthers’ view, the paper argues that Buddhist theories of mind are not “transparent access” accounts. Instead, they not only have an analysis of sensory processing and conscious experience similar to that of ISA, but also share what Carruthers sees as ISA’s central tenet: individuals lack transparent, conscious access to most of their propositional attitudes. Given this fundamental alignment, the Buddhist perspective can offer us fresh responses to ISA’s critics, as well as approaches to ethics and free will that are aligned with ISA’s conclusions.     

The illusion of conscious experience

Synthese - Illusionism about phenomenal consciousness is the thesis that phenomenal consciousness does not exist, even though it seems to exist. This thesis is widely judged to be uniquely...     

How conscious experience and working memory interact

Active components of classical working memory are conscious, but traditional theory does not account for this fact. Global Workspace theory suggests that consciousness is needed to recruit unconscious specialized networks that carry out detailed working memory functions. The IDA model provides a fine-grained analysis of this process, specifically of two classical working-memory tasks, verbal rehearsal and the utilization of a visual image. In the process, new light is shed on the interactions between conscious and unconscious aspects of working memory.     

Intentional action: conscious experience and neural prediction

Intentional action involves both a series of neural events in the motor areas of the brain, and also a distinctive conscious experience that "I" am the author of the action. This paper investigates some possible ways in which these neural and phenomenal events may be related. Recent models of motor prediction are relevant to the conscious experience of action as well as to its neural control. Such models depend critically on matching the actual consequences of a movement against its internally predicted effects. However, it remains unclear whether our conscious experience of action depends on a precise matching process, or a retrospective inference that "I" must have been responsible for a particular event. We report an experiment in which normal subjects judged the perceived time of either intentional actions, involuntary movements, or subsequent effects (auditory tones) of these. We found that the subject's intention to produce the auditory tone produced an intentional binding between the perceived times of the subject's action and the tone. However, if the intention was interrupted by an imposed involuntary movement, followed by the identical tone, no such binding occurred. The phenomenology of intentional action requires an appropriate predictive link between intentions and effects, rather than a retrospective inference that "I" caused the effect.     

Problems in the timing of conscious experience

Libet's (2000) arguments in defense of his interpretation of his experimental results are insufficient. The claims of my critical review (Gomes, 1998) do not suffer with his new statements.     

Reasoning about conscious experience with axiomatic and graphical mathematics

We cast aspects of consciousness in axiomatic mathematical terms, using the graphical calculus of general process theories (a.k.a symmetric monoidal categories and Frobenius algebras therein). This calculus exploits the ontological neutrality of process theories. A toy example using the axiomatic calculus is given to show the power of this approach, recovering other aspects of conscious experience, such as external and internal subjective distinction, privacy or unreadability of personal subjective experience, and phenomenal unity, one of the main issues for scientific studies of consciousness. In fact, these features naturally arise from the compositional nature of axiomatic calculus.     

Against representationalism (about conscious sensory experience)

Abstract

It is very natural to suppose that conscious sensory experience is essentially representational. However this thought gives rise to any number of philosophical problems and confusions. I shall argue that it is quite mistaken. Conscious phenomena cannot be constructed out of representational materials.     

The thalamic dynamic core theory of conscious experience

I propose that primary conscious awareness arises from synchronized activity in dendrites of neurons in dorsal thalamic nuclei, mediated particularly by inhibitory interactions with thalamic reticular neurons. In support, I offer four evidential pillars: (1) consciousness is restricted to the results of cortical computations; (2) thalamus is the common locus of action of brain injury in vegetative state and of general anesthetics; (3) the anatomy and physiology of the thalamus imply a central role in consciousness; (4) neural synchronization is a neural correlate of consciousness.     

Unconscious modulation of the conscious experience of voluntary control

How does the brain generate our experience of being in control over our actions and their effects? Here, we argue that the perception of events as self-caused emerges from a comparison between anticipated and actual action-effects: if the representation of an event that follows an action is activated before the action, the event is experienced as caused by one's own action, whereas in the case of a mismatch it will be attributed to an external cause rather than to the self. In a subliminal priming paradigm we show that participants overestimated how much control they had over objectively uncontrollable stimuli, which appeared after free- or forced-choice actions, when a masked prime activated a representation of the stimuli immediately before each action. This prime-induced control-illusion was independent from whether primes were consciously perceived. Results indicate that the conscious experience of control is modulated by unconscious anticipations of action-effects.     

The mind's best trick: how we experience conscious will

We often consciously will our own actions. This experience is so profound that it tempts us to believe that our actions are caused by consciousness. It could also be a trick, however - the mind's way of estimating its own apparent authorship by drawing causal inferences about relationships between thoughts and actions. Cognitive, social, and neuropsychological studies of apparent mental causation suggest that experiences of conscious will frequently depart from actual causal processes and so might not reflect direct perceptions of conscious thought causing action.     

The neural correlates of conscious experience: an experimental framework

Demonstrating that neural activity ‘represents’ physical properties of the world such as the orientation of a line in the receptive field of a nerve cell is a standard procedure in neuroscience. However, not all such neural activity will be associated with the mental representations that form the contents of consciousness. In some cases, such as when patients with blindsight correctly ‘guess’ the location of a stimulus, neural activity is associated with physical stimulation and with appropriate behaviour, but not with awareness. To identify the neural correlates of conscious experience we need to identify patterns of neural activity that are specifically associated with awareness. Experiments aimed at making such identifications require that subjects report some aspect of their conscious experience either verbally or through some pre-arranged non-verbal report while neural activity is measured. If there is some characteristic neural signature of consciousness, then this should be distinguishable from the kinds of neural activity associated with stimulation and/or behaviour in the absence of awareness. It remains to be seen whether the neural signature of consciousness relates to the location of the neural activity, the temporal properties of the neural activity or the form of the interaction between activity in different brain regions.