Consciousness without a cerebral cortex: A challenge for neuroscience and medicine

2007 ◽  
Vol 30 (1) ◽  
pp. 63-81 ◽  
Author(s):  
Bjorn Merker
Keyword(s):  
Cerebral Cortex ◽  
Brain Stem ◽  
Functional Organization ◽  
Target Selection ◽  
Evolutionary Process ◽  
Conscious State ◽  
Comparative Neurology ◽  
Distributed Information ◽  
Cortical Input ◽  
Vertebrate Brain

A broad range of evidence regarding the functional organization of the vertebrate brain – spanning from comparative neurology to experimental psychology and neurophysiology to clinical data – is reviewed for its bearing on conceptions of the neural organization of consciousness. A novel principle relating target selection, action selection, and motivation to one another, as a means to optimize integration for action in real time, is introduced. With its help, the principal macrosystems of the vertebrate brain can be seen to form a centralized functional design in which an upper brain stem system organized for conscious function performs a penultimate step in action control. This upper brain stem system retained a key role throughout the evolutionary process by which an expanding forebrain – culminating in the cerebral cortex of mammals – came to serve as a medium for the elaboration of conscious contents. This highly conserved upper brainstem system, which extends from the roof of the midbrain to the basal diencephalon, integrates the massively parallel and distributed information capacity of the cerebral hemispheres into the limited-capacity, sequential mode of operation required for coherent behavior. It maintains special connective relations with cortical territories implicated in attentional and conscious functions, but is not rendered nonfunctional in the absence of cortical input. This helps explain the purposive, goal-directed behavior exhibited by mammals after experimental decortication, as well as the evidence that children born without a cortex are conscious. Taken together these circumstances suggest that brainstem mechanisms are integral to the constitution of the conscious state, and that an adequate account of neural mechanisms of conscious function cannot be confined to the thalamocortical complex alone.

Concepts, Conferences, and Controversies

2019 ◽  
pp. 12-31
Author(s):  
Alan J. McComas
Keyword(s):  
Cerebral Cortex ◽  
Brain Stem ◽  
Brain Science ◽  
History Of Research ◽  
History Of ◽  
The Brain

This chapter outlines the history of research meetings dealing with consciousness, beginning with that hosted by Herbert Jasper in the Laurentian mountains of Quebec in 1953. It starts, however, with a brief discussion on ancient scientific approaches to medicine, which was jump-started by the Greek physician, Hippocrates. Afterward, the chapter skips forward two millennia to major figures who made breakthroughs in the field of brain science. It also touches on a central debate that reached its climax a little later, as to which part of the brain was responsible for consciousness. The chapter considers whether it was the cerebral cortex, as had been the prevailing assumption, or if it was the brain stem.

Synthesis

2019 ◽  
pp. 423-472
Author(s):  
Georg F. Striedter ◽  
R. Glenn Northcutt
Keyword(s):  
Functional Organization ◽  
Brain Size ◽  
Brain Regions ◽  
Brain Areas ◽  
Nervous Systems ◽  
Internal Organization ◽  
Vertebrate Brain ◽  
Relative Brain Size

After summarizing the earlier chapters, which focused on the evolution of specific lineages, this chapter examines general patterns in the evolution of vertebrate nervous systems. Most conspicuous is that relative brain size and complexity increased independently in many lineages. The proportional size of individual brain regions tends to change predictably with absolute brain size (and neurogenesis timing), but the scaling rules vary across lineages. Attempts to link variation in the size of individual brain areas (or entire brains) to behavior are complicated in part because the connections, internal organization, and functions of individual brain regions also vary across phylogeny. In addition, major changes in the functional organization of vertebrate brains were caused by the emergence of novel brain regions (e.g., neocortex in mammals and area dorsalis centralis in teleosts) and novel circuits. These innovations significantly modified the “vertebrate brain Bauplan,” but their mechanistic origins and implications require further investigation.

scholarly journals Shape Selectivity in Primate Frontal Eye Field

2008 ◽  
Vol 100 (2) ◽  
pp. 796-814 ◽  
Author(s):  
Xinmiao Peng ◽  
Margaret E. Sereno ◽  
Amanda K. Silva ◽  
Sidney R. Lehky ◽  
Anne B. Sereno
Keyword(s):  
Functional Organization ◽  
Target Selection ◽  
Visual Stimuli ◽  
Shape Selectivity ◽  
Saccade Target ◽  
Frontal Eye Field ◽  
Gaze Shift ◽  
Match To Sample ◽  
Neurophysiological Studies ◽  
Eye Field

Previous neurophysiological studies of the frontal eye field (FEF) in monkeys have focused on its role in saccade target selection and gaze shift control. It has been argued that FEF neurons indicate the locations of behaviorally significant visual stimuli and are not inherently sensitive to specific features of the visual stimuli per se. Here, for the first time, we directly examined single cell responses to simple, two-dimensional shapes and found that shape selectivity exists in a substantial number of FEF cells during a passive fixation task or during the sample, delay (memory), and eye movement periods in a delayed match to sample (DMTS) task. Our data demonstrate that FEF neurons show sensory and mnemonic selectivity for stimulus shape features whether or not they are behaviorally significant for the task at hand. We also investigated the extent and localization of activation in the FEF using a variety of shape stimuli defined by static or dynamic cues employing functional magentic resonance imaging (fMRI) in anesthetized and paralyzed monkeys. Our fMRI results support the electrophysiological findings by showing significant FEF activation for a variety of shape stimuli and cues in the absence of attentional and motor processing. This shape selectivity in FEF is comparable to previous reports in the ventral pathway, inviting a reconsideration of the functional organization of the visual system.

scholarly journals Branching Thalamic Afferents Link Action and Perception

2003 ◽  
Vol 90 (2) ◽  
pp. 539-548 ◽  
Author(s):  
R. W. Guillery
Keyword(s):  
Cerebral Cortex ◽  
Brain Stem ◽  
Visual Pathways ◽  
Perceptual Processing ◽  
Axonal Branching ◽  
Action And Perception ◽  
The Brain ◽  
Anatomical Evidence

Recent observations of single axons and review of older literature show that axons afferent to the thalamus commonly branch, sending one branch to the thalamus and another to a motor or premotor center of the brain stem. That is, the messages that the thalamus relays to the cerebral cortex can be regarded as copies of motor instructions. This pattern of axonal branching is reviewed, particularly for the somatosensory and the visual pathways. The extent to which this anatomical evidence relates to views that link action to perception is explored. Most pathways going through the thalamus to the cortex are already involved in motor mechanisms. These motor links occur before and during activity in the parallel and hierarchical corticocortical circuitry that currently forms the focus of many studies of perceptual processing.

scholarly journals Functional Territories of Human Dentate Nucleus

2019 ◽  
Vol 30 (4) ◽  
pp. 2401-2417 ◽  
Author(s):  
Xavier Guell ◽  
Anila M D’Mello ◽  
Nicholas A Hubbard ◽  
Rachel R Romeo ◽  
John D E Gabrieli ◽  
...  
Keyword(s):  
Cerebral Cortex ◽  
Cerebellar Cortex ◽  
Broad Spectrum ◽  
Neural Control ◽  
Functional Organization ◽  
Neural Processing ◽  
Functional Neuroanatomy ◽  
Default Mode ◽  
Healthy Humans ◽  
Spatio Temporal

Abstract Anatomical connections link the cerebellar cortex with multiple sensory, motor, association, and paralimbic cerebral areas. The majority of fibers that exit cerebellar cortex synapse in dentate nuclei (DN) before reaching extracerebellar structures such as cerebral cortex, but the functional neuroanatomy of human DN remains largely unmapped. Neuroimaging research has redefined broad categories of functional division in the human brain showing that primary processing, attentional (task positive) processing, and default-mode (task negative) processing are three central poles of neural macroscale functional organization. This broad spectrum of human neural processing categories is represented not only in the cerebral cortex, but also in the thalamus, striatum, and cerebellar cortex. Whether functional organization in DN obeys a similar set of macroscale divisions, and whether DN are yet another compartment of representation of a broad spectrum of human neural processing categories, remains unknown. Here, we show for the first time that human DN are optimally divided into three functional territories as indexed by high spatio-temporal resolution resting-state MRI in 77 healthy humans, and that these three distinct territories contribute uniquely to default-mode, salience-motor, and visual cerebral cortical networks. Our findings provide a systems neuroscience substrate for cerebellar output to influence multiple broad categories of neural control.

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