Primary or Idiotypic and Unimodal Early Sensory Cortices

Unimodal and idiotypic systems in the cortex are not essential to sustain a primary consciousness but are clearly essential for normal cognitive and sensory contents. Early sensory cortices are essential for the generation of content in any particular modality, but the evidence suggests that, without "broadcasting" of the conjoint operations of the hierarchy of early and late sensory cortices into heteromodal systems, the content of those sensory operations do not make it into consciousness. Vision is clearly the best mapped of these sensory modalities. Evidence suggests that reentrant communications and various neural synchronies between a host of "early" sensory systems in V1-V4 and "late" ones in V5 are essential to settle the distributed network into a stable "attractor state" that provides a discrete percept. These connectivities may allow "adaptive resonances" (Grossberg, 1980) between top-down conceptual predictions and bottom-up feature detectors, to enable the generation of whole perceptions. Deprived of all connection to early sensory cortices, the brain cannot even hallucinate in that modality. This suggests a conundrum with respect to specification of cortical anatomy and consciousness: We do not need early (primary and unimodal) sensory cortices for a conscious state, or probably for any aspect of core consciousness, but deprived of all early sensory cortices, consciousness would be empty indeed, except perhaps for our affective state (likely quite negative!) and perhaps some degree of proprioception.

NEURAL SUBSTRATES OF CONSCIOUSNESS: IMPLICATIONS FOR CLINICAL PSYCHIATRY TABLE 3.2. Evidence for Global Access or Global Work Space Theories

Results of Results of

Non-Conscious Conscious Conditions

Conditions (Accurately

Source Method (Not-Reportable) Reportable)

Sensory Consciousness

Logothetis et al. multiple studies (e.g.)

Tononi et al. 1999

Srinivasan et al. 1999

Dehaene et al. 2001

Rees et al. 1999

Kjaer et al. 2001

Beck et al. 2002

Binocular rivalry between diagonal contrast edges, color, motion, and objects. Multi-unit recording in visual cortex of the macaque.

MEG of flickering input with binocular rivalry in humans, allowing tracing of input signal with high signal-to-noise (S/N) ratio across large regions of cortex.

As above.

Functional MRI (fMRI) of visual backward masked vs. unmasked words in cortex.

fMRI of unattended and attended words and pictures.

Subliminal vs. supraliminal visual verbal stimuli using PET.

Change blindness vs. change detection.

In early visual cortex 12-20% of cells responded. In object recognition areas inferior temporal & superior temporal sulcus (IT/STS) no cells responded.

Widespread frequency-tagged activation in visual and nonvisual cortex.

In early visual cortex 12-20% of cells responded. In object recognition areas (IT/STS) 90% of cells responded.

50-80% higher intensity in many channels throughout cortex.

Widespread frequency-tagged activation in visual and nonvisual cortex.

Regional activation in early visual cortex only.

Less activation in word/picture areas of visual cortex.

Activation in visual word areas only.

Activation of ventral visual regions including fusiform gyrus.

Higher intensity and coherence in visual and nonvisual cortex.

Higher intensity in visual cortex plus widespread activity in parietal and frontal cortex.

More activation in word/picture areas of visual cortex.

Activation in visual word areas plus parietal and prefrontal cortex.

Enhanced activity in parietal and right dorsolateral prefrontal cortex as well as ventral visual regions.

TABLE 3.2 {continued)

Results of Results of

Non-Conscious Conscious Conditions

Conditions (Accurately

Source Method (Not-Reportable) Reportable)

Vuilleumier et al. 2001

Driver and Vuilleumier 2001

Learning and Practice Haier et al. 1992

Raichle et al. 1999

Mental Effort

John et al. 2001

Seen and unseen faces in visuospatial neglect, using fMRI and event related potentials (ERPs).

unilateral neglect, fMRI, and ERPs.

PET before and after learning computer game Tetris.

Word association vs. simple noun repetition before and after training.

Quantitative EEG (QEEG) for anesthesia vs. waking

Activation of ventral visual regions.

Activation in ventral visual regions including fusiform gyrus.

Drastic drop in cortical metabolic activity.

Trained word association indistinguishable from simple word repetition.

Loss of gamma-band activity, loss of coherence across major quadrants of cortex.

Ventral visual activation plus parietal and prefrontal regions.

Activation also in parietal and frontal areas of the intact left hemisphere.

Widespread, intense cortical metabolic activity.

More intense activity in anterior cingulate, left prefrontal and left posterior temporal lobe and right cerebellar hemisphere.

High prefrontal activation, in middorsolateral, midventrolateral, and dorsal anterior cingulate cortex.

Widespread gamma-band coherence across and within hemispheres.

Extinguished vs. conscious stimuli in

Duncan and Owen Meta-analysis of 10 Low prefrontal 2000 tasks comparing low activation.

and high mental effort (including perception, response selection, executive control, working memory, episodic memory and problem solving).

Waking vs. General Anesthesia

Source : Baars (2002), used with permission of Elsevier.

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