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Consciousness

OBJECTIVES

Objectives

After studying this chapter, the student should be able to:

  • See how biologists believe consciousness evolved on earth from preceding species.

  • Understand the brain structures that support consciousness.

  • Understand the overall function of various cortical areas and their relationship with subcortical structures.

  • See the crucial role of the thalamus in consciousness.

  • Be familiar with the idea of association cortex and the origin of this idea in behaviorist/associationist concepts of perception and knowledge.

  • Be aware of the crucial role of the prefrontal cortex in consciousness and its expansion in humans compared to other mammals and primates.

  • Understand the different functions of lateral prefrontal, ventromedial prefrontal, and anterior cingulate (AC) cortices.

  • Be aware of evidence about consciousness from laterality and split-brain studies.

  • Understand what brain states such as sleep stages and phenomena such as blind sight and neglect indicate about consciousness.

  • Be familiar with theories of consciousness based on mechanisms such as synchronous firing and global brain oscillations.

  • Learn about recent quantum theories of consciousness.

  • Learn about the debate about consciousness and the existence of free will.

A fundamental goal of neuroscience is to understand how consciousness arises in the human brain and how brain damage alters or destroys it. However, studying consciousness is difficult. Consciousness is a subjective inner experience whose content is not measurable using scientific instruments. What can be measured are what are called “correlates” of consciousness—brain activities or activity patterns that occur when consciousness is present compared to the brain activity when consciousness is lost, such as during coma or sleep. If consciousness is defined as an introspective, linguistic-based, inner thought stream that exists only in humans but not in any other animal, then it can only be studied in humans. This ethically precludes virtually all invasive neurophysiologic recording and manipulation techniques except for notable exceptions such as invasive physiologic recordings carried out during epilepsy surgery.

Neuroscientists and philosophers do not all agree with the materialistic idea that consciousness is created by brain activity. Alternative explanations for consciousness range from quantum mechanics to dualistic religious traditions that hold that a nonmaterial soul is the real seat of conscious. In this chapter, we examine aspects of consciousness that we understand depend on neural activity in the brain, such as differences between highly conscious states like normal wakefulness versus sleep or coma, and alterations in consciousness resulting from brain damage.

HOW DID CONSCIOUSNESS ARISE ON EARTH?

Life began on earth about a billion years after its formation 4.5 billion years ago. This life consisted of unicellular prokaryotes such as bacteria. Roughly a billion and a half years later, eukaryotes arose, cells with nuclei. About a billion and a half years after that, complex animals arose during the Cambrian explosion 500 million years ago, giving rise in a few million years to primitive vertebrates. Mammals arose about 200 million years ago, and primates about ...

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