Overview of research: cognitiveneuroscience

Talis Bachmann

3rd Baltic-Nordic Summer School (BNNI 2015), 15.VI 2015

University of Tartu, Institute of Computer Scinece

Computational modeling of brain processes is societally reasonable if pursued in the behaviorally/ clinically meaningful context

This by default necessitates that real data from experimental labs or clinical settings is used as the basis or „reality-check“ for computational modeling

Two basic domains:

1) Encoding of information byneurons and neural nets

2) Decoding of brain signals ofneuronal activity to revealstates, traits, or contents

A. Bottom-up approach capitalizing on the knowledge of the regularities and characteristics of action of individual real neurons mimicked by conceptul model neurons: neuron network input-output F fitting the model with behavior

B. Top-down approach attempting to explain behavioral/brain-imaging phenomena by reducing them to neural processes

The present brief of researchfrom our lab introduces someresults related to both of theseperspectives:

- decoding-related- encoding-related

Main topic: mechanisms ofconsciousness and their neuralsignatures; main exp. approach –contrastive analysis

Decoding-related studies

Brain processes when subject is conscious (of certain content)

Brain processes when subject is not conscious (of certain content)

X + Z signatures

Z signatures

(X+Z) – Z

= X = „NCC“ markers

NCC stands for neural correlates of consciousness, i.e., NCC

An important precondition: stimulation is invariant, but consciousness is a dependent variable

The basic experimental strategy: contrastive

analysis (Baars, 1988; Crick ja Koch, 1993):

Masking, binocular rivalry, attentional blink, crowding, dichotic listening, sleep vs alertness, anesthesia vs alertness, peri-threshold stimulus value (contrast, time, signal-to-noise ratio, …), etc.

necessity to get rid of physical stimulus variability related and target/mask interaction related confounds and importance of differentiating between NCC signatures that are prerequisites for processes indicative of awareness and the signatures directly associated with awareness. Physical variables must not co-vary with C !

Experimental equipment:

Two markers of consciousness:

N200

P300

of the event related potentials (ERPs) obtained in the experimental conditions set up according to the contrastive analysis principle.

General Markers of Conscious Visual Perception and their Timing(submitted)

Renate Rutiku1,2*, Jaan Aru2,3, Talis Bachmann2

1 Institute of Psychology, University of Tartu, Tartu, Estonia2 Institute of Public Law, University of Tartu, Tallinn, Estonia3 Institute of Computer Science, University of Tartu, Tartu, Estonia

Aiming at revealing stimulus-invariant, general ERP-markers of consciousness

TMS/EEG studies extend and complement the „pure“ EEG research by perturbational approach. Causal instead of correlational method. In addition to contents-related NCC, state-related NCC is studied. (Examples follow:)

TMS-evoked activity: NREM sleep vs awake

conscious state is associated with right-central-frontal slow negativity. (Caveat: a recent experiment by Madis

Vasser and Jaan showed somewhat different results, but several aspects of the experiments were different.)

Caffeine vs placebo contrast a reverse

result from the NREM sleep study: caffeine increases negativity

Caffeine increased pre-TMS baseline gamma power; however, it decreased relative power of post-stimulus lower band gamma activity (also: reduction of alpha power about 400 ms post-TMS).

Theoretical article about the so far overlooked confound in NCC research: NCCpr, NCC proper, and NCCco not differentiated.

With contrastive analysis we get not only „true“ NCC, but also markers of neural correlates of prerequisite processes and consequent processes correlating with direct consciousness, but being no markers of constituent, direct consciousness processes

„Reading the mind“ in the perturbational TMS/EEG approach by decoding consciousness contents from TEPs:

Task-irrelevant visual background increased TMS-evoked slow negativity when natural scenes were depicted.

Encoding-related studies

Book: Commack, NY, 1994

Basically, and implicitly, this involves an interaction principle common in coincidence detection microcircuits modeling how specific bottom-up inputs and modulatory inputs interact at the cellular level – viz. the cortical pyramidal neurons (Llinás et al.; Larkum et al.)

An attempt was taken to use the same general principle of temporally delayed SP/NSP interaction, but instead of the single-cell modeling, apply the concept of “retouch” to oscillatory activity of pools of neurons, with implications for binding

Toomas Kirt and Talis exercised modeling how thalamocortical modulations of the oscillatory activity help simulate masking, facilitatory precueing effect, and feature misbinding. (The model included the module allowing zero-lag synchrony between remote oscillators, cf Raul Vicente et al., 2008)

Testing the model with varying SOAs between two successive stimuli. Roughly, the model behave like expected (in terms of relative S1/S2 outputs), but additional motifs seem to be needed for making the functions to increase more with SOA.

Showed individual differnces in metacontrast masking associated with BDNF Val66Met, NRG1/rs6994992, and 5-HTTLPR polymorphisms: no main effects, but several interesting interactions of genetic variables with gender, stage of the sequence of experimental trials, perceptual strategies, and target/mask shape congruence were found. Thus, basic behavioral functions of fast vision may be influenced by common genetic variability. Message: when left uncontrolled, genetic factors may seriously confound variables in vision research using masking, obscureclear theoretical interpretation, lead to unexplicable inter-regional differences and create problems of replicability of formerly successful experiments.

Explored possible relations between polymorphism in 5HTR2A (rs6311) and the functions of metacontrast masking. We found that GG homozygotes performed better with shortest target-to-mask delays, A allele carriers selectively showed the lowest performance level with shortest delays when target and mask stimuli shapes were incongruent and that GG homozygotes' rate of correct perceptiongenerally exceeded that of the A allele carriers. Basic behavioral functions of fast visual discrimination are influenced by common genetic variability. Any masking research with insufficient size of the subjects sample may produce atypical results. It also follows that insofar as certain genes, the expression of which may cause behavioral pathology also influence the results of simple visual masking, masking based tests could be developed for population screening for psychopathological risks.

These genetic variability related studies of behavioral phenotypes in masking may be developed in the direction of computational approaches to neural endophenotype analysis

Thank you for your attention !

(With hopes for human-friendly future IT)