Higher cortical function

• CNS


  Central nervous system
• Spinal cord


  • Most caudal part of CNS
  • Receives sensory information from the skin, joints, and muscles of the trunk and limbs
  • Contains the motor neurons responsible for both voluntary and reflex movements
  • 31 spinal nerves, each of which has a sensory (dorsal root) and a motor (ventral root) division
• Regions of the brain

  • Medulla
  • Pons
  • Midbrain
  • Cerebellum
  • Diencephalon
  • Cerebral hemispheres (telencephalon)
• Brain stem


  • Mediates sensation and motor control of the head, neck, and face
  • Sensory input and motor output carried by 12 cranial nerves
  • Site of entry for information from several specialized senses, such as hearing, balance, and taste
  • Contains ascending and descending pathways that carry sensory and motor information to other divisions of the central nervous system
  • Reticular formation - a relatively diffuse network of neurons distributed throughout the core of the brain stem, receives a summary of much of the incoming sensory information and is important in regulating alertness and arousal
• Cerebellum


  • Considered a purely motor structure until recently
  • Involved in language and other cognitive functions
  • Contains far more neurons than any other single subdivision of the brain, including the cerebral hemispheres (10% of brain weight but 50% of neuronal numbers)
  • Its internal circuitry is well understood because relatively few types of neurons are involved
  • Receives information from the spinal cord about somatic sensation, information from the vestibular organs about balance, and motor and sensory information from various areas of the cerebral cortex via the pontine nuclei
• Diencephalon


  • Thalamus - essential link in the pathway of sensory information from the periphery to sensory regions of the cerebral hemispheres, also interconnects the cerebellum and basal ganglia with regions of the cerebral cortex concerned with movement and cognition, and has regions that are thought to influence levels of attention and consciousness
  • Hypothalamus - regulates homeostasis and several reproductive behaviors, plays an important role in somatic growth, eating, drinking, and maternal behavior by regulating the hormonal secretions of the pituitary Gland, influences behavior through its extensive afferent and efferent connections with practically every region of the central nervous System, and contains the suprachiasmatic nucleus which regulates circadian rhythms
• Anatomical regions of the brain

  • Spinal cord
  • Brainstem
  • Midbrain
  • Pons
  • Medulla oblongata
  • Cerebellum
  • Diencephalon
  • Cerebrum
• Cerebrum


  • Divided into two hemispheres
  • Made up of three basic regions: cerebral cortex, underlying white matter, and several subcortical structures including the basal ganglia
• Cerebral cortex


  • The main functional unit of the cerebrum, a layer of grey matter on the outer surface of the brain that is essential for conscious behaviour
  • Characterized by raised ridges of tissue called gyri, separated by shallow grooves called sulci
  • Grey matter is made up of neuronal cell bodies, dendrites, and axon terminals
  • White matter consists of glial cells and bundles of myelinated axons that relay messages between the cerebral cortex and other parts of the CNS
  • Divided into four major lobes: frontal, parietal, temporal, and occipital
• Basal ganglia


  • Deep below the cerebral cortex, interconnected nuclei involved in the control of movement and aspects of motor learning
• Lobes of the brain

  • Parietal
  • Frontal
  • Occipital
  • Temporal
  • Insula
• Neurosynaptic transmission


  1. Electrical neurotransmission: Action potential generated at origin of axon

  2. Chemical neurotransmission: Action potential reaches axon terminal, stimulates release of neurotransmitters into synaptic cleft, neurotransmitters bind to receptors on postsynaptic neurone, can excite, inhibit or induce other biochemical processes

  3. Neurotransmitters cleared from synaptic cleft by reuptake, diffusion, or enzymatic breakdown
• Higher-Order Functions


  • Performed by the cerebral cortex
  • Involve complex interconnections and communication between areas within the cerebral cortex and between the cerebral cortex and other areas of the brain
  • Involve both conscious and unconscious information processing
  • Not part of the programmed 'wiring' of the brains, therefore subject to modification and adjustment over time (learning)
• Cognition


  Mental processes such as awareness, perception, thinking, knowledge & memory
• Effects of brain lesions

  • Parietal lobe - contralateral neglect syndrome
  • Temporal lobe - agnosia or prosopagnosia
  • Frontal lobe - problems with personality
• Cerebral hemispheres


  • Largest part of the human brain
  • Consist of the cerebral cortex, underlying white matter, and three deep-lying structures: basal ganglia, amygdala, and hippocampal formation
  • Have perceptual, motor, and cognitive functions, including memory and emotion
  • The three subcortical structures act to regulate cortical activity
• Cerebral cortex


  • Thin outer layer of the cerebral hemispheres, responsible for much of the planning and execution of actions in everyday life
  • Divided into four major lobes - frontal, parietal, temporal, and occipital
  • Each lobe includes many distinct functional subregions
  • Cingulate cortex involved in regulation of emotion and cognition
  • Insular cortex concerned with emotion and regulation of homeostasis
• Cortical layers


  • Not all cortex is six-layered neocortex
  • Archicortex has only three or four laminae, regarded as evolutionarily more primitive, hippocampal cortex implicated in acquisition of declarative memories
  • Paleocortex even more primitive, generally has three layers, found on ventral surface of cerebral hemispheres and along parahippocampal gyrus
• Study techniques


  1. Clinical evaluation of brain damaged patients and postmortem correlation

  2. Noninvasive brain imaging methods like diffusion tensor imaging, fMRI, PET

  3. Electrophysiological experiments in non-human primates and other experimental animals
• Lesion studies


  • Provide key insights into the relationship between brain and behavior
  • Observations of the effects of brain injury has led to the development of fundamental concepts
  • Advent of neuroimaging methods has made the precise localization of brain injury in vivo
  • Rest on the assumption that brain injury is eliminative - that it disturbs or eliminates the processing ability of the affected structure
• Complex tasks require integrated processing of component operations that involve many different regions of the brain
• Modern neuroimaging


  • Has brought about a revolution in our understanding of brain function in humans
• Lesion studies


  • Provide key insights into the relationship between brain and behavior
  • Observations of the effects of brain injury has led to the development of fundamental concepts, such as the left hemisphere's dominant role in language and the dependence of visual functions on posterior cortical regions
  • Advent of neuroimaging methods such as computerized tomography (CT) and magnetic resonance imaging (MRI), has made the precise localization of brain injury in vivo
• Lesion studies


  Rest on the assumption that brain injury is eliminative—that brain injury disturbs or eliminates the processing ability of the affected structure
• Modern neuroimaging


  • Revolution in our understanding of brain function in humans has been brought about by the development and widespread availability of novel imaging technologies
  • Positron emission tomographic (PET) is often used to measure local glucose metabolism, which is proportional to neural activity
  • Functional magnetic resonance imaging (fMRI) used to measure local amounts of oxygenated blood
  • Computed tomography (CT) scanning: infarction (stroke), tumors, calcifications, hemorrhage, and bone trauma
  • These techniques provide an index of the level of the activity in various parts of the brain in completely intact healthy humans and in those with different diseases or brain injuries
• Cognitive psychology


  • The study of mental activity as an information-processing problem
  • Cognitive psychologists seek to identify the internal processing—the acquisition, storage, and use of information—that underlies observable behavior
  • A basic assumption of cognitive psychology is that we do not directly perceive and act in the world
  • Rather, our perceptions, thoughts, and actions depend on internal transformations or computations of information obtained by our sense organs
  • Our ability to comprehend that information, to recognize it as something that we have experienced before and to choose an appropriate response, depends on a complex interplay of processes
• Mind is a computer paradigm


  In cognitive psychology
• Cognitive psychology


  • 2 key concepts underlie the cognitive approach:
  • Information processing depends on mental representations
  • Brain derives multiple representations of stimuli. Most basic representation is based on the physical aspects of the stimulus. Second representation corresponds to stimulus identity. Highest level is the stimulus category
  • These mental representations undergo internal transformations
• Cerebral Cortex


  • Surface layer of gray matter -- 3 mm thick
  • Neocortex (six-layered tissue)
  • Newest part of the cortex (paleocortex & archicortex)
  • Layers vary in thickness in different regions of brain
  • 2 types of cells: stellate cells have dendrites projecting in all directions, pyramidal cells have an axon that passes out of the area
• Cortical neuron types


  • Principal (projection) neurons: Cell bodies in layers III, V, VI, Pyramid shaped soma, Glutamate main NT, Long axon
  • Local interneurons: Found in all cortical layers, Spherical soma, GABA main NT, Axon in same layer as soma, 20-25% of neuronal population in neocortex
  • NB: star shaped excitatory found in layer IV with glutamate as NT
• Cortical columns


  • Concept first put forward by Vernon Mountcastle in 1978, described as "the Rosetta stone of neuroscience"
  • Each column is a fraction of a millimeter in diameter
  • Neurons within a column tend to have very similar response properties, because they form a local processing network
  • Columns are thought to be the fundamental computational modules of the neocortex
• Serial processing of sensory information

  1. Each area in the chain carries out certain computations and conveys the results to the next area

  2. In the ventral pathway of the visual system, the pathway begins with neurons that respond to detailed features and proceeds to neurons that encode the overall form

  3. Receptive fields of neurons increase in size from V1 to V4 to inferotemporal cortex

  4. However, sensory pathways not exclusively serial, higher-order areas project back to lower-order areas and modulate their activity
• Parallel processing


  • Same information is processed differently in parallel pathways
  • In the visual system, the dorsal stream processes spatial information and projects to parietal association cortex, the ventral stream processes information about form and projects to temporal association cortex
  • In the auditory and somatosensory systems, dorsal pathways serve motor and spatial functions, ventral pathways serve recognition functions
• Major Connections of the Neocortex

  • Sources of cortical input: Other cortical regions, Hippocampal formation, Amygdala, Thalamus, Brainstem modulatory systems
  • Targets of cortical output: Other cortical regions, Hippocampal formation, Amygdala, Thalamus, Caudate and putamen (striatum), Brainstem, Spinal cord
• Cortical circuitry


  • Each cortical layer has a primary source of inputs and a primary output target
  • Each area has connections in the vertical axis (columnar or radial connections) and connections in the horizontal axis (lateral or horizontal connections)
  • Cells with similar functions tend to be arrayed in radially aligned groups that span all the cortical layers and receive inputs that are often segregated into radial bands or columns
  • Interneurons within specific cortical layers give rise to extensive local axons that extend horizontally in the cortex, often linking functionally similar groups of cells
• Integrative Regions of the Cerebral Cortex

  • Cortical areas that act as centers for complex sensory stimuli and motor responses
  • General interpretive area receives information from all sensory association areas, only present in one hemisphere, usually the left
  • Speech center regulates patterns of breathing and vocalization
  • Prefrontal cortex coordinates information from the secondary and special association areas of the cortex, performs abstract intellectual functions
• Association cortices


  • Regions of cortex where injury causes cognitive deficits that cannot be explained by impairment of sensory or motor function alone
  • Ultimate destination of hierarchical sensory processing
  • Large regions contained within each of the four lobes and contribute to cognition in distinctive ways
  • Parietal association cortex is critical for sensory guidance of motor behavior and spatial awareness
  • Temporal association cortex is important for recognition of sensory stimuli and for storage of semantic (factual) knowledge
  • Frontal association cortex plays a key role in organizing behavior and in working memory
  • Limbic association cortex serves complex functions related to emotion and episodic (autobiographical) memory
• Association cortices


  • Have much more extensive input and output connections than do lower-order sensory and motor areas
  • Some have a variety of visual, auditory, somatosensory, and motor connections that permit them to integrate sensory modalities or to use sensory information to guide motor behavior
  • All association areas are interconnected by a dense network of pathways within and between the parietal, temporal, frontal, and limbic lobes
• Association cortices connectivity


  • Thalamic inputs transmit sensory and motor information that has already been processed in the primary sensory and motor areas of the cerebral cortex and is being fed back to the association regions
  • Enrichment in connections from other cortical areas, called corticocortical connections, can be intrahemispheric or interhemispheric (via corpus callosum, anterior commissure)
  • Another important source of innervation to the association areas is subcortical, arising from the dopaminergic, noradrenergic, serotonergic, and cholinergic nuclei, important for learning, motivation, and arousal
• Temporal association cortex


  • Major function is the recognition and identification of stimuli that are attended to, particularly complex stimuli
  • Patients with agnosia acknowledge the presence of a stimulus but are unable to report what it is
  • Agnosias have both a lexical aspect (a mismatching of verbal or other cognitive symbols with sensory stimuli) and a mnemonic aspect (a failure to recall stimuli when confronted with them again)