Module 8 Flashcards
How are the sensory areas of the cortex classified?
By convention, the sensory areas of the cortex are classified into three types: primary, secondary, and association.
What defines the primary sensory cortex of a system?
The primary sensory cortex of a system is the area that receives most of its input directly from the thalamic relay nuclei of that system.
What is the secondary sensory cortex of a system?
The secondary sensory cortex comprises the areas that receive most of their input from the primary sensory cortex of that system or from other areas of secondary sensory cortex of the same system.
Define association cortex.
Association cortex is any area of cortex that receives input from more than one sensory system, with most input coming via areas of secondary sensory cortex.
What are the three major principles characterizing the interactions among sensory areas?
The three principles are hierarchical organization, functional segregation, and parallel processing.
Describe hierarchical organization in sensory systems.
Sensory systems are hierarchically organized based on the specificity and complexity of their function, with each level adding another layer of analysis before passing information up the hierarchy.
What characterizes the effects of damage to various levels of the sensory hierarchy?
The higher the level of damage, the more specific and complex the sensory deficit, with destruction of receptors resulting in a complete loss of ability to perceive in that sensory modality.
What is functional segregation?
Functional segregation refers to the organization of sensory systems into functionally distinct areas at each level of cerebral cortex, specializing in different kinds of analysis.
What is parallel processing in sensory systems?
Parallel processing refers to the simultaneous analysis of a signal in different ways by multiple parallel pathways of a neural network, indicating that sensory systems are parallel rather than serial.
What are top-down signals in sensory systems?
Top-down signals are information flows from higher to lower levels of sensory hierarchies, in addition to the more common bottom-up information flow.
What is the primary function of the auditory system?
The primary function of the auditory system is the perception of sound.
What range of molecular vibrations can humans hear?
Humans can hear molecular vibrations between about 20 and 20,000 hertz (cycles per second).
What are the three main perceptual dimensions of sound vibrations?
The amplitude, frequency, and complexity of sound vibrations are most closely linked to perceptions of loudness, pitch, and timbre, respectively.
What is Fourier analysis?
Fourier analysis is the mathematical procedure for breaking down complex waves into their component sine waves.
How is pitch perception related to the fundamental frequency of a sound?
The pitch of a sound is related to its fundamental frequency, which is the highest common divisor of the various component frequencies making up the sound.
What is the missing fundamental in pitch perception?
The missing fundamental refers to the perception of a pitch that is not directly related to the frequency of any individual component of a complex sound.
Describe the pathway of sound waves through the ear.
Sound waves travel from the outer ear down the auditory canal, causing the tympanic membrane to vibrate. These vibrations are then transferred to the ossicles of the middle ear, which in turn transmit the vibrations to the cochlea via the oval window.
What is the organ of Corti?
The organ of Corti is the auditory receptor organ located within the cochlea, composed of hair cells that respond to vibrations.
How are different frequencies represented along the basilar membrane?
Different frequencies produce maximal stimulation of hair cells at different points along the basilar membrane, with higher frequencies activating hair cells closer to the windows and lower frequencies activating hair cells at the tip of the basilar membrane.
What is tonotopic organization?
Tonotopic organization refers to the arrangement of auditory structures according to frequency, similar to retinotopic organization in the visual system.
How does the auditory pathway to the cortex differ from the visual pathway?
There is no major auditory pathway to the cortex comparable to the retina-geniculate-striate pathway in the visual system. Instead, there is a network of auditory pathways involving the cochlear nuclei, superior olives, inferior colliculi, medial geniculate nuclei, and primary auditory cortex.
Where do the axons of the auditory nerve synapse after entering the brainstem?
The axons of the auditory nerve synapse in the ipsilateral cochlear nuclei.
What is the role of the superior olives in the auditory pathway?
The superior olives combine signals from each ear and transmit them to both ipsilateral and contralateral auditory cortex.
Why are the subcortical pathways of the auditory system considered complex?
The subcortical pathways of the auditory system have many more synapses compared to other senses, which contributes to their complexity.
Where is the primary auditory cortex located in primates?
The primary auditory cortex in primates is located in the temporal lobe, hidden within the lateral fissure.
What are the three adjacent areas comprising the core region of the primary auditory cortex?
The three adjacent areas comprising the core region of the primary auditory cortex are: A1, the anterior auditory field (AAF), and the rostral field (R).
How is the primary auditory cortex organized?
The primary auditory cortex is organized in functional columns, tonotopically (by frequency), and according to the temporal components of sound, known as periodotopy.
What is the tonotopic organization of the auditory cortex?
Each area of the auditory cortex has a gradient of frequencies from low to high along its length.
What is periodotopy?
Periodotopy refers to the organization of auditory cortex according to variations in the amplitude of particular sound frequencies over time.
How has recent progress in understanding human auditory cortex been achieved?
Recent progress in understanding human auditory cortex has resulted from the convergence of functional brain-imaging studies in humans and invasive neural recording studies in monkeys.
Why has research on auditory cortex lagged behind research on visual cortex?
One major reason is a lack of clear understanding of the dimensions along which auditory cortex evaluates sound.
What is one example of an output signal from auditory cortex relevant to an animal’s current situation?
The creation of representations of auditory objects, such as converting the complex mixture of frequencies produced by a piano into a sound representation that allows recognition of the instrument.
What are the two main cortical streams of auditory analysis proposed by researchers?
The anterior auditory pathway, more involved in identifying sounds (what), and the posterior auditory pathway, more involved in locating sounds (where).
What is the traditional assumption about sensory system interactions in association cortex?
Association cortex is usually defined as areas where interactions or associations between sensory systems take place.
Where have functional brain imaging studies found evidence of sensory interactions?
Functional brain imaging studies have found evidence of sensory interactions at the lowest level of the sensory cortex hierarchy, in areas of primary sensory cortex.
What has recent research discovered about the perception of pitch in auditory cortex?
Most auditory neurons respond to changes in frequency rather than pitch; however, a small area anterior to primary auditory cortex has been identified as the likely place where frequencies of sound are converted to the perception of pitch.
What is the missing fundamental technique used in auditory research?
The missing fundamental technique involves using sound stimuli where frequency and pitch are different, revealing how auditory neurons respond to pitch.
What technique did Bendor and Wang (2005) use to identify the area responsible for perceiving pitch?
They used microelectrodes to probe primary and secondary areas of monkey auditory cortex and found a small area anterior to primary auditory cortex that responded to pitch rather than frequency.
How has research on auditory processing shifted based on recent discoveries?
Research now suggests that sensory system interaction is an early and integral part of sensory processing, occurring not only in association cortex but also at the lowest level of the sensory cortex hierarchy.
Why is the study of damage to the auditory system important?
It provides information about how the auditory system works and can serve as a source of information about the causes and treatment of clinical deafness.
What is the major permanent effect of bilateral lesions to the primary auditory cortex?
Loss of the ability to process the structural aspects of sounds, leading to a condition often referred to as “word deafness.”
What are the consequences of damage to the anterior auditory cortex pathway (the “what” pathway)?
Patients have trouble identifying sounds.
What are the consequences of damage to the posterior auditory cortex pathway (the “where” pathway)?
Patients have difficulty localizing sounds.
How prevalent is deafness as a human disability?
Deafness affects an estimated 360 million people worldwide and is one of the most prevalent human disabilities.
What are the two common classes of hearing impairments?
Conductive deafness, associated with damage to the ossicles, and nerve deafness, associated with damage to the cochlea or auditory nerve.
What is the major cause of nerve deafness?
Loss of hair cell receptors in the cochlea.
How do age-related hearing loss affect speech perception in elderly individuals?
It leads to difficulty distinguishing high frequencies, causing challenges in understanding sounds like “s,” “f,” and “t.”
What is tinnitus, and what is its association with hearing loss?
Tinnitus is ringing in the ears, often associated with hearing loss. Neuroplastic changes resulting from deafness are believed to cause tinnitus.
How do cochlear implants help individuals with nerve deafness?
Cochlear implants bypass damage to the auditory hair cells by converting sounds into electrical signals, which excite the auditory nerve.
What is the significance of early cochlear implantation after deafness onset?
The sooner a person receives a cochlear implant after becoming deaf, the more likely they are to benefit, as disuse leads to alterations of the auditory neural pathways.
An area of the cortex that receives input from multiple sensory systems and integrates sensory information is called the _______ cortex.
association
Sensation is the process of detecting the presence of stimuli, and the higher-order process called _______ allows the interpretation of sensory patterns.
perception
The simultaneous analysis of signals, also known as _______ processing, allows for information to flow through multiple pathways at the same time.
parallel
In the 1960s, the sensory organization was believed to be hierarchical, _______ _______, and serial.
functionally homogeneous,
The frequency of sound vibrations is linked to perceptions of _______.
pitch
Sound waves travel from the external environment to the outer ear, and through the auditory canal where they reach the _______ membrane.
tympanic
The three smallest bones in the human body are the malleus, the incus, and the _______.
stapes
The _______ are auditory receptors located in the cochlea on the basilar membrane, and they increase firing in axons of the auditory nerve.
hair cells
Axons from olivary neurons project to the _______ _______ via the lateral lemniscus.
inferior colliculi
The cochlea and the primary auditory cortex are both organized _______ on the bases of sound frequencies.
tonotopically
Damage to the ossicles is associated with _______ deafness, while damage to the cochlea is associated with _______ deafness.
conductive, nerve
The anterior auditory pathway is more involved in identifying sounds (what), whereas the _______ auditory pathway is more involved in locating sounds (where).
posterior
What are sensations from the body referred to as?
Somatosensations.
How many separate systems make up the somatosensory system?
Three separate but interacting systems: exteroceptive, proprioceptive, and interoceptive.
What are the divisions of the exteroceptive system?
Divisions for perceiving mechanical stimuli (touch), thermal stimuli (temperature), and nociceptive stimuli (pain).
What are the four types of cutaneous receptors?
Free nerve endings, Pacinian corpuscles, Merkel’s disks, and Ruffini endings.
What are Pacinian corpuscles sensitive to?
Sudden displacements of the skin but not to constant pressure.
How do Merkel’s disks and Ruffini endings respond to stimuli?
They adapt slowly and respond to gradual skin indentation and skin stretch, respectively.
What happens when a constant pressure is applied to the skin regarding receptor firing?
Initially, all receptors respond, but after a few hundred milliseconds, only the slowly adapting receptors remain active, leading to a change in the quality of sensation.
What is stereognosis, and how does it relate to receptor adaptation?
Stereognosis is identifying objects by touch. Receptor adaptation ensures that the pattern of stimulation continually changes during object manipulation.
How do somatosensory receptors respond to stimuli?
Stimuli deform or change the chemistry of the receptor, altering the permeability of the receptor cell membrane to various ions, resulting in a neural signal.
Initially, what was assumed about each type of receptor in the skin regarding tactile sensations?
It was assumed that each type of receptor mediated a different tactile sensation (e.g., touch, pain, heat).
What has research shown about tactile sensations and receptor mechanisms?
Each tactile sensation appears to be produced by the interaction of multiple receptor mechanisms, and each receptor mechanism contributes to multiple sensations.
How many major pathways carry somatosensory information to the human cortex?
Two major pathways: the dorsal-column medial-lemniscus system and the anterolateral system.
What type of information does the dorsal-column medial-lemniscus system tend to carry?
Information about touch and proprioception.
What type of information does the anterolateral system tend to carry?
Information about pain and temperature.
What happens to touch perception and proprioception if the dorsal-column medial-lemniscus system is lesioned?
Lesions of the dorsal-column medial-lemniscus system do not eliminate touch perception or proprioception.
What happens to pain and temperature perception if the anterolateral system is lesioned?
Lesions of the anterolateral system do not eliminate perception of pain or temperature.
How do sensory neurons of the dorsal-column medial-lemniscus system enter the spinal cord?
Via a dorsal root.
What is the role of the ventral posterior nucleus of the thalamus in the dorsal-column medial-lemniscus system?
It receives input from dorsal column nuclei neurons and projects to the primary somatosensory cortex (SI).
What is a trivia-worthy fact about dorsal column neurons originating in the toes?
Dorsal column neurons originating in the toes are the longest neurons in the human body.
How do most dorsal root neurons of the anterolateral system synapse?
Most synapse as soon as they enter the spinal cord.
What happens if both ascending somatosensory paths are completely transected by a spinal injury?
The patient can feel no body sensation from below the level of the cut.
Who mapped the primary somatosensory cortex in 1937 during neurosurgery?
Penfield and his colleagues.
What did Penfield discover about the human primary somatosensory cortex (SI)?
It is somatotopic, organized according to a map of the body surface.
What is the somatotopic map of the body surface commonly referred to as?
The somatosensory homunculus.
Where is the secondary somatosensory cortex (SII) located in relation to the primary somatosensory cortex (SI)?
Just ventral to SI in the postcentral gyrus, extending into the lateral fissure.
What body parts receive the greatest proportion of input in the somatosensory homunculus?
Hands, lips, and tongue.
What is the primary input pattern for SII?
SII receives substantial input from both sides of the body.
What evidence supports columnar organization in the primary somatosensory cortex?
Studies of single neurons found that each neuron in a particular column responds most robustly to the same type of tactile stimuli on the same part of the body.
How many functional strips compose the primary somatosensory cortex?
Four functional strips, each with a similar but separate somatotopic organization.
What are the proposed streams of analysis that proceed from SI?
A dorsal stream to posterior parietal cortex for multisensory integration and direction of attention, and a ventral stream to SII for the perception of objects’ shapes.
What were the observed deficits in patients after a unilateral excision that included SI?
Reduced ability to detect light touch and identify objects by touch (stereognosis).
Where are somatosensory signals ultimately conducted in the sensory hierarchy?
To areas of association cortex in prefrontal and posterior parietal cortex.
What type of neurons are found in posterior parietal cortex?
Bimodal neurons, which respond to activation of two different sensory systems.
What is astereognosia?
The inability to recognize objects by touch.
What is asomatognosia?
The failure to recognize parts of one’s own body.
What is contralateral neglect?
The tendency not to respond to stimuli that are contralateral to a right-hemisphere injury.
