The workshop was succesfully held with 12 talks, 40 posters and more than 200 participants. Thank you very much.

[Abstract] (In alphabetical order)

Ralph Adolphs

"The Amygdala's Role in Consciousness of Emotions"

The amygdala has long been highlighted as a structure intimately involved in emotion, specifically fear. In particular, it has been thought to be involved in two components of emotion processing: (1) very rapid, automatic, non-conscious emotional processing, such as detection of fearful facial expressions; (2) expression and experience of emotions. Building on an emerging literature on the connectivity and electrophysiology of the amygdala, and presenting new data from our own laboratory, I will argue that these views need to be modified. Point (1) is not correct as originally conceived, since complete lesions of the amygdala in humans still preserve many aspects of non-conscious emotion processing. Point (2) needs to be modified as well; I will argue that the amygdala may trigger many components of an emotional response, but that it is not likely to be a necessary part of the neural correlate of the conscious experience of emotions.

Ned Block

"Three Theories of Consciousness"

Comparison of the three major theories of consciousness taken seriously by neuroscientists, the global workspace theory, the higher order theory and the biological theory. Clarifies what the difference is between these theories and describes the advantages and disadvantages of each. Considers both conceptual and empirical arguments for and against the major theories. Argues that the biological approach is better able to handle the “explanatory gap”, the fact that nothing that is now known allows us to understand why the neural basis of an experience is the neural basis of that particular type of experience rather than another type of experience or, instead, a non-experiential state.

Olivia Carter

"How do neurotransmitters help decide what we see?"

One pervading mystery in neuroscience is the question of how the brain is able to generate an "internal" perceptual experience from the available "external" sensory information. Ambiguous stimuli, like binocular rivalry and the Necker cube, offer a unique means to investigate this process experimentally because observers generally experience changes between multiple perceptual states without corresponding changes in the stimulus. I will present results obtained using a variety of methods including pharmacology (hallucinogens), pupillometry and basic psychophysics. The data relates primarily to vision, but I will also describe recent studies looking at auditory and tactile rivalry. Together the results suggest that the cycle of perceptual switching characteristic of rivalry may reflect a generalized mechanism that allows the brain to decide between multiple valid alternatives, without becoming stuck on a non-optimal decision. While the exact mechanisms are unknown, my data, and research from other groups, suggest that the process may depend heavily on the coordinated activity of defuse neurotransmitter systems like serotonin and noradrenaline. Because I wish to claim that this mechanism is common to the domains of perception, attention and action, I will conclude by briefly discussing my results in relation to current theories of behavioral decision making.

John-Dylan Haynes

"Decoding consciousness"

Despite many years of research on the neural correlates of consciousness (NCCs), it is still unclear how the detailed contents of consciousness are represented in the human brain. It is often assumed that specific contents of consciousness are encoded in dedicated core NCCs - one for each different aspect of conscious experience. Due to their low spatial and temporal resolution conventional approaches to human neuroimaging are severely limited in their ability to reveal such content-selective mechanisms. Now, the approach of multivariate decoding provides a powerful framework for studying the relationship between consciousness and content-selective processing in more detail. This approach makes it possible to assess how conscious experience is encoded in the brain, and how the encoding of sensory information is affected when it enters awareness.

Ryota Kanai

"Neurostructural correlates of individual difference in the switch rate of perceptual rivalry"

When the visual system is confronted with ambiguous stimuli, the perceptual interpretation spontaneously alternates between competing interpretations. It has been known that the rate of perceptual switch varies considerably across individuals. Although numerous studies have examined the neural substrates involved in spontaneous perceptual switches, the origin of the individual difference in switch rate has not yet been estabilished. Here, we investigated neurostructural markers of individual's switch rate by examining how cortical thickness, local gray matter volume and fractional anisotropy (FA) correlate with individual's switch rate for a bistable, rotating structure-from-motion sphere. Our analysis revealed that cortical thickness of the left intraparietal sulcus (IPS) and the volume of bilateral IPS positively correlate with individual's switch rate. Furthermore, we found that the FA values of the white matter tracts providing connections to and from the bilateral IPS correlate positively with individual's switch rate. In order to establish that the neurostructural correlates in the IPS plays a causal role in perceptual switch, we modulated the activity of the IPS using transcranial direct current stimulation (tDCS) and compared changes in the switch rate before and after the tDCS. The results showed that suppression of IPS slows perceptual switch rates, confirming the causal involvement of IPS in perceptual switches. Taken together, these results demonstrate a direct relationship between neurostructure of the IPS and individual's switch rate.

Christof Koch

"On the Relationship between the Consciousness and Attention"

The relationship between attention and consciousness is a close one, leading many scholars to conflate the two. My talk summarizes psychophysical evidence arguing that top-down attention and consciousness are distinct phenomena that need not occur together and that can be manipulated using distinct paradigms (Koch & Tsuchiya 2007; Tsuchiya & Koch 2008). Subjects can become conscious of an isolated object, or the gist of the scene in the near absence of top-down attention. Conversely, subjects can attend to perceptually invisible objects. In particular, I will describe a full factorial study of the influences of attention and consciousness (as assayed by visibility) on afterimage formation (van Boxtel, Tsuchiya & Koch 2009). We investigated the duration of the afterimage for all four combinations of an attended/unattended and visible/invisible grating and demonstrated that selective attention and visual consciousness have opposite effects: paying attention to the grating decreases the duration of its afterimage, while consciously seeing the grating increases afterimage duration. These data provide clear evidence for distinctive influence of attention and consciousness on visual perception. Such dissociations between attention and consciousness become easier to understand when considering the different functions of these two processes. Untangling their tight relationship is a necessary step in the scientific elucidation of consciousness and its material substrate.

Hakwan Lau

"The dynamic threshold hypothesis for sensory awareness"

Most theories assume that sensory awareness happens when the relevant neural signal passes a certain threshold; weak signals are subliminal and strong signals yield conscious percepts. The key contention here is that such threshold is not fixed. Rather, the brain adjusts this threshold dynamically in order to achieve statistical optimality. Therefore, the same signal strength can actually lead to awareness or unawareness, depending on whether the threshold is low or high respectively. This prediction has been confirmed in clinical cases of blindsight, as well as by psychophysical experiments in normal volunteers. Behaviorally, signal strength can be estimated by forced-choice task performance index d’. When d’ was matched across conditions in an fMRI experiment, awareness was reflected by activity in the prefrontal cortex, but not by the early visual areas. In another experiment, transcranial magnetic stimulation applied to the prefrontal cortex changed the subjective reports of awareness without changing forced-choice task performance. Computational analysis suggests that reports of awareness depend on a late-stage of information processing in a hierarchy, rather than a special “conscious” channel. Activity in the prefrontal cortex is likely to reflect processing at this late stage. Finally, in psychophysics experiments we showed that top-down spatial attention changed both the signal strength for a visual stimuli as well as its threshold. Therefore, in some cases, the lack of attention could paradoxically lower task performance but boost awareness. This may explain why we seem to have an inflated sense of phenomenology for unattended objects at the periphery. Taken together, these results suggest that, despite common research practice, forced-choice task performance may not reflect the most interesting aspects of sensory awareness, as it could be systematically decoupled from subjective reports of conscious experience.

Shin'ya Nishida

"Psychophysical approach to the measurement of perceptual latency"

There is always a time lag between detection of physical signals by a sense organ (e.g., photoreceptors on the retina) and establishment of the corresponding perceptual representation (or perceptual awareness) in the observer’s brain. Despite past extensive investigation, our current understanding of the perceptual latency is far from complete.

One cannot easily specify the perceptual latency in the time course of evoked neural activity without knowing the neural correlate of perception. Since perception is a subjective experience, one might expect that perceptual latency should be best estimated from the observer’s subjective judgment on apparent timing, such as simultaneity and temporal order. However, subjective temporal judgments should be considered as the brain’s interpretation of the time course of the physical events that does not faithfully reflect of the neural latency for perception [1]. Several findings suggest the existence of the mechanisms in the brain that make subjective time judgments veridical (e.g., temporal judgments based on time markers [2], and adaptive recalibration of simultaneity [3]).

A more promising index of perceptual latency is the behavioral response latency for a perceptual decision, since it gives objectively measurable time that surely includes the latency of the observer’s brain to reach a certain perceptual decision. In addition, when successfully correlated with simultaneously measured neural response, the behavioral latency could suggest when and where in the brain the perceptual decision is made [4,5].

To psychophysically investigate how perceptual latency is determined, we measured behavioral reaction time to judge perception of bistable stimuli. Our results suggest that perceptual ambiguity has little effects on perceptual latency [6], and that a predictive/postdictive modulating stimulus alters the perceptual latency in a timing-dependent manner [7]. A coherent account of the obtained data can be given by an independent race model in which the perceptual evidence is independently accumulated for alternative perceptual interpretations.

[1] Dennett, D. C. & Kinsbourne, M. Behav Brain Sci 15, 183-247 (1992).
[2] Nishida, S. & Johnston, A. Curr Biol 12, 359-368 (2002).
[3] Fujisaki, W. et al. Nat Neurosci 7, 773-778 (2004).
[4] Cook, E. P. & Maunsell, Nat Neurosci 5, 985-994 (2002)
[5] Amano, K. et al. J Neurosci 26, 3981-3991 (2006).
[6] Takei, S. & Nishida, S. Vision (Vision Society of Japan), 21(3) (2009)
[7] Takei, S. et al. Vision (Vision Society of Japan), 21(2) (2009)

Naotsugu Tsuchiya

"Neuronal activity in area MT during perceptual stabilization of ambiguous structure-from-motion"

While viewing an ambiguous stimulus, such as binocular rivalry, perception spontaneously alternates between two alternatives. Ambiguous stimuli are powerful tools to study the neuronal correlates of consciousness as they allow us to study the neuronal activity that fluctuates along with conscious percept while physical inputs remain the same. Despite prior studies using ambiguous stimuli, little has been known as to what kind of neuronal activity supports perceptual switches and maintains one perceptual interpretation for a sustained time.

Perceptual alternation can be greatly slowed down if the stimulus is periodically removed from view, a phenomenon called ‘perceptual stabilization’ (Leopold et al NatNeuro 2002): a handy model for studying the detailed dynamics of perceptual switches and perceptual memory. Here, we presented ambiguous structure-from-motion stimuli to awake monkeys and recorded neuronal activity from area MT with multiple (>10) electrodes under two conditions differing in the strength of perceptual stabilization. Using multivariate decoding techniques (Tsuchiya et al PLoSONE 2008), we could decode the percept during stimulus presentation (~70% correct) but we could not predict upcoming percepts before stimulus presentation in both conditions. Most notably, the latency of MT decoding was much faster in the condition with strong stabilization. Our results suggest that MT is responsible for “encoding” of perceptual memory, but it is not actively involved in its “maintenance”. MT primed during stabilization, resulting in faster latency.

Melanie Wilke

"Thalamo-cortical interactions underlying spatial awareness and decision making"

While sensory responses in cortex and thalamus have been studied extensively, little is known about the role of thalamo-cortical interplay related to visual awareness. With a combined approach of behavioral experiments, pharmacology and fMRI in monkeys, we are attempting to identify processes related to visual awareness. Previous electrophysiological experiments had revealed that spiking responses in the thalamic pulvinar, but not the LGN, are correlated with conscious perception of visual stimuli as reported by monkeys (Wilke et al., 2009).

Consequently, pulvinar inactivation in these monkeys led to spatial neglect symptoms such as target detection failures and directional hand, head and eye movement bias. Based on these results and the strong anatomical interconnections of the pulvinar with visual and parietal cortical areas, we hypothesized that the pulvinar contributes to spatial awareness by modulating activity in cortical areas related to spatial attention and decision making. To study effects of pulvinar inactivation on activity in the widespread cortical network, we combined pharmacological inactivation of the pulvinar with functional MRI in monkeys performing spatial decision tasks.

Specifically, we reversibly inactivated pulvinar while a monkey performed a delayed memory saccade to either an instructed location (‘single target’ condition) or was free to choose between two spatial alternatives (‘two target’ condition). Consistent with spatial neglect behavior, pulvinar inactivation did not impair memory saccade performance towards single targets, but led to a pronounced choice bias towards targets in the ipsilesional visual hemifield in the two target condition. The monkey performed the task in the 4.7T MRI scanner while we measured BOLD activity before and after pulvinar inactivation. Pulvinar inactivation reduced BOLD activity in many cortical regions within the injected hemisphere, including the lateral bank of the intraparietal sulcus (IPS, i.e. LIP) and multiple areas in the superior temporal sulcus (STS). At the same time, activity in cortical areas in the opposite hemisphere was modestly elevated. Taken together, our results suggest that the thalamic pulvinar is critically involved in spatial perception and decision making and may fulfill this function by modulating activity in temporo-parietal cortical areas.

Takamitsu Yamamoto

"Cerebrospinal stimulations therapy for the treatment of vegetative state and minimally conscious state"

【Introduction】The Multi-Society Task Force on PVS (1994) summarized the medical aspects of the vegetative state. They provided a statement that the VS is a clinical condition of complete unawareness of the self and the environment, accompanied by sleep-wake cycles, with either complete or partial preservation of hypothalamic and brainstem autonomic function. However, there are various grades of severity and various stages leading to various outcomes, even if the patient displays neurological signs identical to the VS. The definition of the minimally conscious state (MCS) is characterized by inconsistent but clearly discernible behavioral evidence of consciousness and can be distinguished from coma and the VS by documenting the presence of specific behavioral features. We evaluated patients in the VS and MCS by an electrophysiological approach, and compared with the results of cerebrospinal stimulation therapy.

【Methods】 Forty-one cases of a vegetative state (VS) caused by various kinds of brain damage were evaluated neurologically and electrophysiologically at 3 months after brain injury. These cases were treated by deep brain stimulation (DBS) therapy or spinal cord stimulation (SCS), and followed up for over 10 years. The mesencephalic reticular formation was selected as a target in 2 cases, and the thalamic centre median-parafascicular (CM-pf) complex was selected as a target in the other 19 cases. SCS was applied in other 20 cases.

【Results】Ten of the 41 patients emerged from the VS, and became able to obey verbal commands. In the 10 cases that emerged from the VS, the Vth wave of the ABR and N20 of the SEP were recorded even with a prolonged latency; continuous EEG frequency analysis demonstrated a desynchronization pattern or slight desynchronization pattern; and the pain-related P250 was recorded with an amplitude of over 0.007mV. However, they remained in a bedridden state except for 1 case. On the other hand, DBS and SCS achieved consistent discernible behavioral evidence of consciousness, and emergence from the bedridden state in 10 of 12 minimally conscious state (MCS) patients.

【Conclusion】Cerebrospinal stimulation therapy can be a useful method for the treatment of prolonged coma patients, if candidates are correctly selected with electrophysiological evaluation.

Masatoshi Yoshida

"What-it-is-like of monkey with blindsight"

We examined awareness in monkeys with unilateral V1 lesions and sought neural activity specific to blindsight. First, we examined whether the monkeys are able to maintain short-term memory of the stimuli presented in their contralateral ('affected') hemifield. The monkeys were tested with a memory-guided saccade task with a 2 sec-delay. The success ratio was over 80%, significantly higher than chance. Then we recorded the neuronal activity from the superior colliculus (SC) during the memory-guided saccade task. We found that a majority of the neurons recorded from the ipsilesional SC showed a sustained activity selective for spatial locations of targets. These results suggest that the monkeys with V1 lesion retain a certain level of visual awareness and that it was represented in the SC. Then we examined their visual awareness more directly using comparison between the performance of a forced-choice (FC) task, in which localization of target positions was required, and that of a yes-no (YN) task, in which detection of the targets was required. The performance of the YN task indicates residual detection in the affected hemifield. Single-unit recording from the SC revealed that, in the ipsilesional SC, the neural response to the visual stimuli in the affected hemifield was larger when the monkeys successfully detect the targets than when the monkeys missed them. Finally, we examined decision process of these monkeys using a forced-choice (FC) task. We modeled the distribution of saccadic reaction times by a modified diffusion model and obtained evidence that the decision threshold in the affected hemifield was lower than that in the normal hemifield. These results suggest that V1 lesion affect awareness and decision and that neural activity in the SC is a neural correlate of reduced awareness.

Maintained by Masatoshi Yoshida (NIPS)
Last update: Aug 6, 2009