Concurrent session III

Sunday June 22, 2:00PM-4:00PM

  • CS 3.1. Mary Revisited
  • CS 3.2. Blindsight in Normal and Lesioned Brains
  • CS 3.3. Anaesthesia and Coma

 

CS 3.1. Mary Revisited

Chair: Ian Gold

An Examination of No-Concept Reply to Frank Jackson's Knowledge Argument

Yasuko Kitano, Philosophy, Hosei University, Japan

In recent years, one of the most widely debated questions in the philosophy of mind has been whether consciousness is physical or nonphysical. Frank Jackson's Knowledge Argument, which argues that there are truths about consciousness that cannot be deduced from physical truths and draws the conclusion that physicalism is false, has attracted much interest since its appearance in 1982. In this paper, I examine Benj Hellie's No-Concept Reply (hereafter NCR) to the argument, and present another version of NCR.

The power of the knowledge argument as an argument derives from the intuition that no amount of non-phenomenal knowledge suffices for phenomenal knowledge (empiricism about phenomenal knowledge). The major physicalist explanations of the alleged physical-phenomenal gap that have been presented so far, in regard to what the object of the phenomenal knowledge in question is, tend to fall into two camps: (A) those which regard it as a fact of the instantiation of phenomenal redness, and (B) those which regard it as something other than facts (such as the acquisition of ability or acquaintance). NCR is classified as (A). According to David Chalmers, NCR holds that a truth stating that phenomenal redness is instantiated can be deduced from a physical megatruth a priori in that it is knowable a priori by anyone who possesses the concepts involved in those truths. To this reply, Chalmers has presented the objection that it is not clear that the relevant concepts alone can close all relevant epistemic gaps. I point out that there is another option which may be adopted. If, as I believe, the object of the phenomenal knowledge in question is not a fact of the instantiation of phenomenal redness as an occurrent property, but a fact of the exercise of the capacity, or 'power,' to see red, then it is less clear that the physical-phenomenal gaps blocking the deduction still remain because a capacity is to be infallibly exercised if certain conditions for its exercise are met. Furthermore it does not seem to me that the knowledge argument as it is rules out such a dispositional account of phenomenal knowledge.

  • Keywords: knowledge argument, consciousness, phenomenal concepts
  • Corresponding Email: yasukos@sannet.ne.jp
  • Presentation: Talk, Sunday June 22, 2:00PM-4:00PM at Locke Hall

 

Cognition and Consciousness

Nicholas Georgalis, Department of Philosophy, East Carolina University, USA

I distinguish two concepts often conflated: representation and information bearing. I argue that representation requires conscious and is intentional (is about or directed at objects or states of affairs). Information bearing does not require consciousness, and it is not intentional. This has consequences for the distinction between conscious and unconscious beliefs. Strictly there are no unconscious beliefs though there are information bearing states, lacking intentionality, that are systematically related to conscious beliefs, which are intentional.1

What are called ‘unconscious beliefs’ or ‘unconscious representations’ are innocently understood as a certain types of information bearing states, states that one has while asleep, otherwise unconscious, or conscious but thinking about other things. These states enable occurrent conscious belief states, but are neither representational nor intentional themselves. As such, they expose important features and relations of the basis for cognition, but not of cognition itself. If I am right about this, it would go far in explaining why there has been so much success in studies of cognition that ignore consciousness, even while consciousness is necessary for representation and ultimately for cognition itself. These studies succeed when they focus on unconscious states, which most assuredly are integral to the success of cognitive activities, and which are falsely assumed to have representational features of conscious states.

It is a grave error, therefore, and one that is frequently made, to infer from such successes that results pertaining to unconscious “beliefs” or “representations” are transferable to conscious beliefs and representations, or when it is thought that these successes show that consciousness itself is epiphenomenal or not central to cognition. These errors are based on the deeply flawed, but widely held, assumption that the sense of belief and representation employed in discussions of conscious and unconscious states is the same. If I am right, this assumption is false. That conscious beliefs are representational while the related but unconscious states are not is an important but unnoticed difference that goes far in both resolving and explaining some of the deep divisions in the literature as to the relevance of consciousness and the first-person perspective to investigations of cognition.

A corollary is that Frank Jackson’s refutation of his earlier Knowledge argument fails. It depends in part on the assumption that representational facts are in principle derivable from micro-physical facts. This assumption is false on the view advanced in my 2006.

1 Extensive arguments for these claims are presented in my book, The Primacy of the Subjective: Foundations for a Unified Theory of Mind and Language, Bradford Book, MIT Press, 2006.

  • Keywords: representation, information bearing conscious/unconscious, intentionality
  • Corresponding Email: georgalisn@ecu.edu
  • Presentation: Talk, Sunday June 22, 2:00PM-4:00PM at Locke Hall

 

Trouble with Dretske's Accessibility

Karen Yan, Department of Philosophy, The Johns Hopkins University, USA

Ned Block (2007) argues for the empirical separation of phenomenology and accessibility partly based on the Sperling paradigm and the change blindness paradigm. Block’s thesis states that the cognitive accessibility underlying reportability is not a constitutive part of phenomenology. Interestingly, Fred Dretske (2004, 2006) interprets the two paradigms in a similar manner to Block’s, though his view of phenomenology is contrary to Block’s. Both of them interpret the subjects in the two paradigms as being conscious of more than what they can report. Yet while Block argues for the separation of phenomenology and accessibility, Dretske treats phenomenology as a special kind of accessibility. Block however acknowledges that “there is phenomenology without accessibility in one sense of the term but not another (p.18).” That is, Block leaves open the bare possibility that some sense of accessibility could have necessary relations to phenomenology.

Thus, one may argue that Dretske’s special sense of accessibility could be the one intrinsic to phenomenology as Block acknowledges. In this paper, I will argue against the above with the following three claims: First, Dretske’s accessibility is inadequate to substantiating the claim that one is conscious of more than one can report. Second, Dretske’s accessibility shares a common theoretical commitment with global accessibility. Third, given that the above two claims hold, Dretske’s accessibility cannot be intrinsic to phenomenology as Block construes it.

  • Keywords: Dretske, Block, Accessibility, Phenomenology, Sperling paradigm, Change Blindness
  • Corresponding Email: karenruyuyan@gmail.com
  • Presentation: Talk, Sunday June 22, 2:00PM-4:00PM at Locke Hall

 

What It Is Like to Think. On Cognitive Phenomenology, Functionalism, and Externalism

Marius Dumitru, Philosophy, University of Oxford, UK

The very idea of cognitive phenomenology is considered by many as a non-starter, because of a definitional restriction of phenomenology to non-cognitive states. But perhaps we should clarify the intension of the concept first and determine its extension on that basis, and not start with an exclusivist extension followed by the assignment of a concept to it. It seems to me that the concept of phenomenology allows cognitive phenomenology in its extension.

If we agree on the cogency of the very idea of cognitive phenomenology, there is a further question about its specification. One could hold that cognitive phenomenology just is a) the phenomenology of inner speech (Carruthers 2006, Jackendoff 2007) or b) the phenomenology of mental images, emotions, or feelings (of effort, conviction, understanding, etc.) conjured by thoughts. Fringe phenomenology (such as the tip-of-the-tongue phenomenon) may challenge the specification in terms of the phenomenology of inner speech. It seems to me that even if we bracket a) and b), which are typically present, we are still left with a phenomenological core: the phenomenology of cognitive meaning. Many authors (among others, G. Strawson, Siewert, Pitt) converge on a specification of cognitive phenomenology in terms of grasp of intentional contents and the experience of semantic comprehension, while others (Horgan & Tienson, B. Loar) emphasize the grounding of all content in a phenomenal basis (mental paint for Loar). I agree with a specification in terms of the experience of semantic comprehension, with the qualification that we should not consider it simpliciter, but as the end product of a complex process involving the mastery of conceptual structures.

My claim is that if there is intrinsic cognitive phenomenology, it has to be functionally exhausted to a great extent. Arguments are presented against exclusively equating it with the phenomenology of inner speech, and the feelings of comprehension and conviction, on the ground that these phenomenal aspects engender certain anomalies if considered separately as accounting for the phenomenology of thoughts.

Functional exhaustion for the case of cognitive phenomenology is shown to be immune to inverted spectra and absent qualia objections, because from the point of view of inferential involvement, colour concepts are constructs derived from experience, and zombie arguments are not free from prior assumptions of separability between functional and phenomenal aspects in the case of thoughts.

This specification of cognitive phenomenology in (narrow) functionalist terms may entail an internalist view of mental content.

  • Keywords: Cognitive phenomenology
  • Corresponding Email: marius.dumitru@chch.ox.ac.uk
  • Presentation Website: http://users.ox.ac.uk/~chri2904
  • Presentation: Talk, Sunday June 22, 2:00PM-4:00PM at Locke Hall

 

CS 3.2. Blindsight in Normal and Lesioned Brains

Chair: Zoltan Dienes

Neural Correlate of Reduced Visual Awareness in the Superior Colliculus of Monkeys with Blindsight

Masatoshi Yoshida, Department of Developmental Physiology, National Institute for Physiological Sciences, Japan
Kana Takaura, Department of Developmental Physiology, National Institute for Physiological Sciences, Japan
Tadashi Isa, Department of Developmental Physiology, National Institute for Physiological Sciences, Japan

It has been reported that macaque monkeys with unilateral lesions in V1 exhibited analogous behavior to the human blindsight patients (Cowey and Stoerig, 1995). Here we examined behavioral report of visual awareness in monkeys with unilateral V1 lesions using saccade tasks 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 delay activity selective for spatial locations of targets. On the other hand, the ratio of neurons with a delay activity was lower in the contralesional SC. 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 FC task was better than that of the YN task when stimuli were presented in the affected hemifield. Such a dissociation of performance was not observed when stimuli with low luminance contrasts were presented in the ipsilateral ('normal') hemifield, indicating that the dissociation is specific to the V1 lesion, not a general phenomena occurring in near-threshold vision. Then we examined whether the neural activity of SC during the YN task is dependent on the monkeys' report on visual awareness. We found 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. Such modulation was not found in the neural response to the near-threshold stimuli in the normal hemifield when we recorded from the contralesional SC. These results suggest that the modulation of neural activity found in the ipsilesional SC is a neural correlate of reduced visual awareness that specifically induced by V1 lesion.

* Keywords: residual vision, neuron, near-threshold vision, implicit perception
* Support: KAKENHI 13854029, 16700343 and CREST
* Corresponding Email: myoshi@nips.ac.jp
* Presentation: Talk, Sunday June 22, 2:00PM-4:00PM at Socrates Hall

 

Motion Induced Blindness: The More You Attend the Less You See

Olivia Carter, Department of Psychology, Harvard University, USA
Robert Luedeman, Department of Psychology, Harvard University, USA
Stephen Mitroff, Department of Psychology, Duke University , USA
Ken Nakayama, Department of Psychology, Harvard University , USA

During motion induced blindness (MIB), visually salient objects vanish from awareness when presented on a background of coherent motion. Here we investigate the influence of attention on the perceptual disappearance of an individual stimulus target by systematically changing the number of stimulus items, grouping categories and the attentional demand at a central fixation task. In Experiment One, 1-4 square targets (varying in color and angular rotation) were each presented centered within one of the four visual quadrants. When a single target was presented alone it was visibly suppressed for 23.4% of the 40 second trials. Surprisingly, the disappearance of the same target was reduced by more than half to an average of 11.4% of the trial when additional targets were presented. In Experiment Two, the effect of group number was considered. In every trial, all 4 target squares were presented within the same quadrant. Targets defined as “in group,” shared feature properties (color, texture, proximity and alignment of border contours), “out-group” targets differed in respect to all features. Despite only moderate effects of the grouping cues (i.e., simultaneous disappearance of all 4 targets only increased from 0.5% when targets formed 4 out-groups to 2% when targets formed a single group), an increase in group number lead to greater total disappearance without any associated increase in the disappearance of the individual targets. In Experiment Three, we selectively manipulated attentional load with a central detection task. Subjects reported less disappearance of a single target in high attention conditions relative to fixation and low attention conditions. In all experiments, a simulated MIB condition ruled out the effect of task difficulty or response inaccuracy. Together these results indicate a striking paradox: the more attention allocated towards a target object, the more that object will be suppressed from awareness. A number of mechanisms are considered to explain this surprising effect.

  • Keywords: Vision, Awareness, Perception, Attention, Suppression, Motion-Induced-Blindness
  • Corresponding Email: ocarter@wjh.harvard.edu
  • Presentation: Talk, Sunday June 22, 2:00PM-4:00PM at Socrates Hall

 

TMS on Intraparietal Sulcus Triggers Perceptual Disappearance

Ryota Kanai, Institute of Cognitive Neuroscience, University College London, UK
Neil Muggleton, Institute of Cognitive Neuroscience, University College London, UK
Vincent Walsh, Institute of Cognitive Neuroscience, University College London, UK

During a prolonged fixation, visual objects presented in the periphery of visual field often fade from awareness. This phenomenon has been largely attributed to adaptation of neurons responding to peripheral targets. However, it has been found that even without a prolonged adaptation, a brief presentation of transient stimuli is effective for inducing the perceptual disappearance.

We hypothesized that perceptual disappearance might result from degeneration of feedback from attention-related cortical areas to early visual areas, and visual transients disrupt the feedback loop to sustain low-level signals and thereby trigger perceptual fading. We examined this hypothesis by briefly disrupting the functions of attention-related regions in the intraparietal sulcus (IPS) using transcranial magnetic stimulation (TMS). The hypothesis predicted that a brief disruption of IPS would trigger perceptual disappearances, as does a visual transient.

We measured perceptual disappearance by asking participants to discriminate the presence or absence (fading) of a peripheral green target immediately after a TMS pulse. On half of trials the target remained on the screen until the end of a trial, and on the other half of trials it gradually faded. On trials where the target physically remained on the display, “present” and “absent” responses were counted as hit and miss, respectively. Likewise, on trials where the target physically faded, “present” and “absent” responses were counted as and false alarm and correct rejection, respectively.

The results of a no-TMS condition showed that presentation of a flash reduced the hit rate without affecting the false alarm rate, and correspondingly a decrease in sensitivity (d’) and a shift of decision bias (c and β) was observed. Consistent with the effect of visual flash, TMS on IPS decreased the hit rate but the false alarm rate was unaffected compared with the control conditions with TMS on vertex. This suggests that TMS on IPS had a similar pattern of effect on the visibility of the peripheral target. In particular, the decrease in the hit rate shows that observers reported disappearance of the target more frequently when their IPS was interfered with TMS. These results suggest that IPS is involved in sustaining perception in continuous viewing.

  • Keywords: visual awareness, TMS, parietal, fading
  • Support: Human Frontier Science Program Foundation
  • Corresponding Email: kanair@gmail.com
  • Presentation: Talk, Sunday June 22, 2:00PM-4:00PM at Socrates Hall

 

Visual Awareness Correlates with Layer-Specific Activity in Visual Cortex

Alexander Maier, UCNI; Laboratory of Neuropsychology, NIH, USA

The role for primary visual cortex (V1) in establishing and maintaining the perceptual outcome of sensory stimulation is a matter of longstanding debate. Part of the reason is that neuroimaging studies in humans and monkeys suggested strong activity changes whenever a stimulus goes unperceived, whereas single neuron recordings in the same area have found only little effect. A possible link between these results has recently been suggested by neurophysiological experiments that demonstrated robust perceptual modulation in V1 in the low frequency range (< 30Hz) of the local field potentials (Wilke et al., 2006).
Here we investigate the nature of these percept-related neuronal signals by means of layer-specific multi-channel recordings in primary visual cortex of trained macaque monkeys during visual suppression. We recorded the laminar profile of V1 local field potentials (LFPs) as well as single and multiunit activity in two animals that either perceived or did not perceive a salient visual target stimulus that was placed in the receptive field region of nearby neurons. This approach permitted us to examine the laminar profile of spiking, evoked potential, voltage power modulation, transient current source density (CSD), and sustained current source power. The latter two quantities are thought to reflect membrane currents that can be localized in cortical depth. Each of these quantities was evaluated using both broadband LFP signals within a restricted range of frequencies.
We found that the local field and current sources varied in their responses to perceptual suppression as a function of their laminar position. The CSD analysis revealed prominent differences in the upper layers related to the transient target disappearance. Sustained power changes in both the field potential and localized currents varied in their laminar profile for the different frequency ranges tested.
The diminished supragranular activity during perceptual suppression, which resembles that of the fMRI signal, may reflect a disruption of synaptic input corresponding to feedback from the extrastriate cortex or a modulatory signal of subcortical origin.

  • Keywords: NCC visual awareness binocular rivalry V1
  • Support: NIH Intramural Program
  • Corresponding Email: maiera@mail.nih.gov
  • Presentation Website: http://www.alex-maier.info
  • Presentation: Talk, Sunday June 22, 2:00PM-4:00PM at Socrates Hall

 

CS 3.3. Anaesthesia and Coma

Chair: Jen-Chuen Hsieh

Unconsciousness and the Energy Consumption of Brain During Resting State

Feiyan Chen, Physics Department, Zhejiang University, China
Xiaolan Song, Physics Department, Zhejiang University, China
Xiaowei Tang, Physics Department, Zhejiang University, China

Functional magnetic resonance imaging (fMRI) and PET have been widely used to investigate the neural basis of human cognition such as perception, attention, memory, emotion, and so on. Majority of such studies focused on what happened in the brain during a specific goal-oriented task Recently, there have been increasing interests in the brain’s activities during resting state. Many experiments have suggested that there is ongoing intrinsic activity in the brain which is related to information processing and accompanied by large energy consumption during resting state. Without reasonalble explanation of this phenomenon, the large energy consumed by the brain during resting state is named of “Dark Energy”.
In this article we discuss the characteristic of unconsciousness and review some studies about the brain’s intrinsic activity during resting state and energy consumption. Then, we put forward the viewpoint that the large energy consumption of brain during resting state is devoted into unconscious activity. We argue that (1) unconsciousness is the process of durative information processing in the brain rather than a state; (2) besides it’s implicit effect on behavior, ongoing intrinsic unconscious activity consumes substantive energy of brain; (3) we should foucus on the psychological meaning of unconsciousness as well as the neural correlates and the physiological meaning of unconsciousness.

  • Keywords: unconsciousness, energy consumption, brain, resting state
  • Support: “985” Foundation of Zhejiang University
  • Corresponding Email: fmrilab@zju.edu.cn
  • Presentation: Talk, Sunday June 22, 2:00PM-4:00PM at Plato Hall

 

Resting State Connectivity Integrity in the Default Network Reflects the Level of Consciousness Impairment in Brain-Injured Patients. An fMRI Study in Brain Death, Coma, Vegetative State, Minimally Conscious State and Locked-In Syndrome

Melanie Boly, Coma Science Group, Cyclotron Research Centre, University of Liege, Belgium
Audrey Vanhaudenhuyse, Coma Science Group, University of Liege, Belgium
Luaba Tshibanda, Cyclotron Research Centre, University of Liege, Belgium
Marie-Aurelie Bruno, Radiology Department, University of Liege, Belgium
Pierre Boveroux, CHU Sart Tilman Hospital, University of Liege, Belgium
Quentin Noirhomme, Coma Science Group, University of Liege, Belgium
Caroline Schnakers, Cyclotron Research Centre, University of Liege, Belgium
Athena Demertzi, Coma Science Group, University of Liege, Belgium
Didier Ledoux, Cyclotron Research Centre, University of Liege, Belgium
Bernard Lambermont, Coma Science Group, University of Liege, Belgium
Gusatve Moonen, Cyclotron Research Centre, University of Liege, Belgium
Robert-Ferdinand Dondelinger, Coma Science Group, University of Liege, Belgium
Christophe Phillips, Cyclotron Research Centre, University of Liege, Belgium
Pierre Maquet, Coma Science Group, University of Liege, Belgium
Steven Laureys, Cyclotron Research Centre, University of Liege, Belgium

The ‘default network’ is defined as a set of areas, encompassing posterior-cingulate/precuneus, anterior cingulate/mesiofrontal cortex and temporoparietal junctions, showing more activity at rest than during attention-demanding tasks. This network has been involved in higher cognitive functions like self-related processes, emotion, and memory. Recent studies have shown that it is possible to reliably identify this network in healthy volunteers in the absence of any task, by resting state connectivity analyses. The aim of this study was to test if the integrity of resting-state connectivity in the default network would differ in different pathological alterations of consciousness. Thirteen acutely brain damaged patients in brain death (BD; n=1), coma (5), vegetative state (VS; 3), minimally conscious state (MCS; 3) and locked-in syndrome (LIS; 1)) and 12 healthy controls participated to the study. Patients were assessed using the Coma Recovery-Scale Revised. For each subject, a 10 minutes resting-state acquisition was performed. Data were analysed using independent component analysis (ICA) and statistical parametric mapping (SPM). A goodness-of-fit comparison was performed (Greicius et al. PNAS 2004; 101 : 4637-42) on individual subjects’ Z maps, taking the control group’s default network as a template. Our analysis searched for differences in the selected components between controls and patients groups. Mean goodness-of-fit scores for individual default network components were respectively 1.25 for controls, 1.22 for LIS, 1.15 for MCS patients, 0.79 for VS and 0.77 for coma. In the BD patient, no cortical spatial map could be identified. Significantly less activity was observed within all areas of the default network for coma and vegetative state patients as compared to controls. Locked-in and minimally conscious patients were not significantly different from controls. Finally, all default network areas connectivity was shown to be linearly correlated with the degree of clinical consciousness impairment of the patients, ranging from coma, to vegetative state, minimally conscious state and locked-in syndrome. Our data show that default network connectivity is decreased in severely brain-damaged patients, in proportion to their degree of consciousness impairment. Ongoing work on a larger patient cohort is currently performed, aiming to evaluate the prognostic value of the presented methodology.

  • Keywords: functional MRI, coma, vegetative state, resting state, consciousness
  • Support: Belgian National Fund for Scientific Research (FNRS)
  • Corresponding Email: A.Demertzi@student.ulg.ac.be
  • Presentation Website: http://www.comascience.org
  • Presentation: Talk, Sunday June 22, 2:00PM-4:00PM at Plato Hall

 

Diversity of Conscious Experiences During General Anaesthesia

Valdas Noreika, Centre for Cognitive Neuroscience, University of Turku, Finland

It seems that the anaesthesiological definition of consciousness as behavioural responsiveness to external stimuli does not fully match the neurophilosophical concept of consciousness as the presence of subjective experiences. Apparently, the loss of responsiveness is dissociated from continuation of subjective experiences. Several studies have confirmed dreaming during anaesthesia, which is a paradoxical but definite sign of subjective contents of consciousness in a state when conscious experiences are typically believed to be absent. In the present study, we aimed to describe the diversity of conscious experiences occurring during general anaesthesia. 58 experimental sessions were conducted during which subjects were anaesthetized with either dexmedetomidine, propofol, sevoflurane or xenon. After awakening, reports of subjective experiences were collected in a structured interview. 59 % of anaesthesia sessions resulted in reports of conscious experiences, which were further analyzed with the Scale for Conscious Experiences during Anaesthesia: experiences ranged from simple bodily sensations to visual and auditory imagery, and from elements of anaesthesia awareness to complex dreams. Further, several EEG measures, such as spectral entropy and BIS Index, were used to contrast the presence and the absence of conscious experiences during anaesthesia. Results confirm that the presence of subjective experiences is compatible with clinically defined anaesthesia as a loss of behavioural responsiveness. Thus, studies aiming to investigate the loss of consciousness should additionally control whether it is really phenomenal consciousness that is lost, or merely behavioural responsiveness. Further theoretical and methodological implications will be discussed, such as the difficulties of relying on first-person reports in studies investigating the neural mechanisms of anaesthesia and consciousness, as well as the status of anaesthesia awareness, a condition when patients report remaining aware during the operation. This raises the hypothesis that in at least some of these cases, what appear to be reports of anaesthesia awareness may actually be the result of hallucinatory anaesthesia dreaming.

  • Keywords: loss of consciousness, anaesthesia dreaming, anaesthesia awareness
  • Corresponding Email: valnor@utu.fi
  • Presentation: Talk, Sunday June 22, 2:00PM-4:00PM at Plato Hall

 

The Effects of Anaesthetics on the Cortex as Revealed by Voltage Sensitive Dye Imaging

Michael R. H. Hill, Department of Pharmacology, Oxford University, UK
Susan A. Greenfield, Department of Pharmacology, Oxford University, UK

This presentation consists of an introduction to voltage sensitive dye imaging (VSDI) and anaesthetics as well as a short digression on why the in vitro mouse brain slice is an excellent tool for the scientific investigation of consciousness. This is followed by a methods and a results section concluding with a look at how the study of anaesthetics in general and our findings specifically may contribute to the science of consciousness.

As a result of technical limitations neuroscience today is split into two main areas of investigation. On the one side there is the microscopic world of cellular interactions in the realm of micrometers and milliseconds. On the other side there are macroscopic investigations in the form of MRI and PET studies with a maximum resolution of millimetres and seconds. However, many people believe that consciousness is realized somewhere in between, at the level of large networks of neurons interacting with each other on a sub-second timeframe. With the help of VSDI we now have a tool at hand, which allows us to start exploring this realm and thus slowly close the gap between the very large and the very small and the very fast.
The aim of the study presented here was to better understand how anaesthetics interact with the brain at the level of large network dynamics. In a mouse brain slice containing the thalamocortical connections electrical stimulation of the relevant nucleus in the thalamus results in activation of the primary somatosensory cortex. We recorded this activity with VSDI over a large area of cortex with a temporal resolution of 1000 Hz over 850 ms. In order to determine the effects of general anaesthetics on these large scale neuronal network dynamics we added the anaesthetics Ketamine, Propofol, Thiopental and Etomidate to the bath solution respectively. The obtained data was analyzed separately for each layer of cortical activity as to be able to precisely localize the positive and negative correlations between the various conditions. Our data thus gives insight into the general way anaesthetics, with often very different chemical and biological properties, affect the circuitry upon which consciousness supervenes.

  • Keywords: consciousness, anaesthetics, voltage sensitive dye imaging, electrophysiology, local field potentials, cortex, mouse
  • Corresponding Email: michael.hill@pharm.ox.ac.uk
  • Presentation: Talk, Sunday June 22, 2:00PM-4:00PM at Plato Hall