Kandel: Functional Organization of Perception and Movement

Question 1

Thalamus (1): Role and what its made up

Answer 1

Thalamus conveys sensory input to primary sensory areas of cerebral cortex
“more of a gatekeeper than a relay station”
Prevents or enhances passage of specific information depending on the behavioral state

Made up of many well-defined nuclei. Some receive information specific to a sensory modality and project to a specific area of the isocortex. Others participate in motor functions, transmitting information from cerebellum to motor regions of frontal lobe

There are four groups of nuclei in the thalamus, with respect to the INTERNAL MEDULLARY LAMINA that runs the rostro-caudal length of the thalamus -> medial group is located medial to internal medullary lamine, ventral and posterior groups are lateral to it

Question 2

Thalamus (2): Thalamic nuclei (groups)

Answer 2

following thalamic nuclei are relay (or specific) nuclei because they have a selective relationship with a particular cortical portion

Anterior group: receives input from mammilary nuclei of hypothalamus, plays role in memory and emotion

Medial group: receives input from portions of basal ganglia, amygdala and midbrain, implicated role in memory

Ventrolateral group: important for motor control and carry information from basal ganglia and cerebellum to motor cortex
Ventral posterior lateral nucleus conveys somatosensory information to isocortex

Posterior group: includes the medial and lateral geniculate nucleus, lateral posterior nucleus, and the pulvinar
Pulvinar: is extensibely interconnected with widespread regions of parietal, temporal, occipital lobes
- medial: component of auditory system, organized tonotopically, conves auditory information to superior temporal gyrus
- lateral: receives information from retina and conveys it to primary visual cortex

Question 3

Thalamus (3): thalamus does not only…

Answer 3

… project to visual areas of isocortex but also receives return inputs back from the isocortex. Nonspecific thalamic nuclei project to several cortical and subcortical regions and are located either in the midline of thalamus or within medullary lamina

Question 4

Thalamus (4): Intralaminar nuclei

Answer 4

project to medial temporal lobe structures such as amygdala and hippocampus, also project to components of basal ganglia
receive inputs from spinal cord, brain stem and cerebellum
thought to mediate cortical arousal

Question 5

Thalamus (5): Reticular Nucleus

Answer 5

The reticular nucleus is the outer covering of the thalamus

Majority of its neurons use GABA, wheras most neurons in other thalamic nuclei use glutamate
Neurons are not interconnected with isocortex, their axons terminate on other thalamic nuclei -> reticular nucleus modulates activity in other thalamic nuclei based on monitoring of the entirety of the thalamocortical stream of information

–> This portion of the thalamus acts like a filter that gates information flow to the isocortex

Question 6

Sensory Information Processing in the Cerebral Cortex

• -> humunculus
• -> functional organization
• -> somatosensory cortex

Answer 6

Neurons in different parts of the cortex are somatotopically organized
All parts of body are represented in cortex somatotopically, but area of cortex devoted to each body part is NOT proportional to its mass
Cortical area devoted to each body part is proportional to the densitiy of innervation = the fineness of discrimination in the body part

Cerebral cortex is organized functionally into columns of cells  which each compromise a computational module with a highly specialized function
The larger the cortical area dedicated to a function, the greater the number of computational collumns dedicated to that functions
e.g.: the highly discriminative sense of touch in the fingers is due to the large area of cortex dedicated to processing somatosensory information from the hand

The somatosensory cortex contains several somatotopic maps of the body surface

Processing of sensory information in the cerebral cortex begins with primary sensory areas, continues in unimodel association areas, and is completed in multimodel association areas

Question 7

Voluntary Movement (1)

Answer 7

Voluntary movement requires coordination of all components of the motor system. The principle components are the motor cortex, basal ganlia, thalamus, midbrain, cerebellum, and spinal cord

Primary motor cortex is also organized somatotopically, so specific regions of motor cortex influence the activity of specific muscle groups

Motor information from cerebral cortex, passing midbrain, pons and medulla, carried in corticospinal tract is modulated by both sensory information and information from other motor regions

A continuous stream of tactile, visual and proprioceptive information is needed to make voluntary movement

The output of the motor cortex is under the substantial influence of other motor regions, including CEREBELLUM and BASAL GANGLIA wich are both reposnible for the smooth execution of skilled movements and important for motor learning

Question 8

Voluntary Movement (2): Cerebellum

Answer 8

Receives somatosensory information directly from primary afferents from spinal cord and from corticospinal axons descending from the isocortex
Thought to be part of ERROR-CORRECTING MECHANISM for movements
- can compare movement commands from cortex with somatic sensory information about what actually happened
- important in PREDICTIVE CONTROL OF MOVEMENTS: commands for movements are adjusted based on information about the effectiveness of prior movement
Enables motor control systems to adapt motor commands to changing conditions
The cerebellum’s major influence is through its connections in the ventrolateral nuclei of the thalamus, which connect directly to the motor and premotor cortex

Question 9

Voluntary Movement (3): Basel Ganglia

Answer 9

= collection of subcortical nuclei

Receive direct projections from much of isocortex, including sensory, motor, and premotor areas
Send signals to regions of thalamus that project to cerebral cortex
Dysfuncitons of basel ganglia result in particularly striking disorders of movement characteristic of Parkinson’s and Huntington’s
- The abnormal signal send by dysfunctional basal ganlgia to cortical motor areas have a major, negative, impact on motor output