What are the 3 main components of the brain
- forebrain (cerebral hemispheres and diencephalon)
- midbrain
- hindbrain (medulla, pons, cerebellum) (form connections between the brain and spinal cord)
Unimodal Cortex
- processing information pertaining to a specific sensory modality
- prominent role in perception
Polymodal Cortex
- processes information received from disparate modalities through afferent connections (arriving)
- critically involved in higher-order conceptual processes that are less dependent on concrete sensory information than on abstract features extracted from multiple inputs
- e.g., includes convergence zones of the anterior temporal lobe and inferior parietal lobule
Frontal lobe is broken down into three different areas:
- orbitofrontal/ventromedial region: emotion regulation, reward monitoring, personality (orbitofrontal damage - disinhibition; ventromedial damage- disordered reward/punishment processing, problems learning experiences with reward value and emotional significance)
- dorsolateral region: broad range of cognitive-executive functions (damage- dysexecutive syndromes- impaired working memory, poor attention to control behavior)
- dorsomedial region: intentional and behavioral activation (damage akinetic mutism - person is alert and awake (not comatose) but cannot move or speak)
Temporal Lobe 3 regions:
- temporal polar cortical areas: intersensory integration and semantic memory (words/concepts/numbers)
- ventral temporal areas: object recognition (damage -object and face agnosia)
- posterior temporal region: (middle and superior temporal sulci) primary auditory areas and Wernicke’s area in language- dom hem- important for language comprehension, prosodic (prosody) comprehension in the non-dom hemisphere
Parietal lobe 3 areas:
- superior parietal lobe: sensory-motor integration, body schema, spatial processing
- temporoparietal junction: phonological and sound based processing; laungauge comprehension (left) music comprehension (right)
- inferior parietal lobule: complex spatial attention, integration of tactile sensation, self-awareness
Occipital Lobe:
Primary visual Cortex
Visual Association Cortex -
Complete vs Partial Damage
- complete damage produces cortical blindness or phenomena of Anton’s syndrome (denial of cortical blindness) or blindsight (detection of unconsciously perceived stimuli in the blind field
- Partial damage -visual field defects
Ventral Visual Pathway
connecting occipital and temporal lobe; important for object and face recognition, item based memory, and complex visual discrimination
Dorsal Visual pathway
connecting the occipital and parietal lobes via the superiro temporal sulcus; importatn for spatial vision and visuomotor integration
Neuroanatomy of Vision
retinal ganglion cells –> optic nerve–> projects posteriorally and comes together at the optic chiasm
Majority of optic tract fibers terminate in the lateral geniculate nucleus (LGN) of the thalamus –>primary visual cortex in broadmann area (17) - striate cortex in theoccipital pole
- this geniculostriate pathway is critial for visual discrimination and form perception
- extrageniculate or extrastriate visual pathway- small proportion of fibers bypass the LGN and terminate in the pretectal area and superior colliculus –> project to broad areas of the parietal and frontal association cortex (frontal eye fields BA 8) via relays in the pulvinar nucleus of the thalamus
- tectopulvinar system- pupillary light reflex, attention-directed eye movements, general orientation to visual stimuli, more sensitive to movement that to form
Vision:
Dorsal pathway
Ventral pathway
projects to the parieto-occipital association cortex
- processes spatial information
- involved in visuomotor interaction (e.g., reaching, manipulating objects)
- lesions: problems with spatial perception, attention, visuomotor processing (e.g., hemispatial neglect, impaired visual reaching)
projects to occipitotemporal association cortex –>anterior portions of inferotemporal cortex
- processes structural and feature-based information- helps with analysis and recognition of visual form (faces/objects)
- lesions: perceptual disturbances , (severe) rec of familiar objects and faces (agnosias)
Vision:
apperceptive vs associative agnosia
apperceptive: impairment in processing basic visual elements of the object (shape, contour, depth)
- damage extensive to the visual association areas
associative: relating a well perceived stimulus to stored representations based on prior experience with the stimulus
- damage-less extensive or disconnecting lesions in regions between association cortex and memory
Neuroanatomy of Memory: Temporal Lobe Structures
Hippocampus
Hippocampus (dentate gyrus, sectors of Ammon’s horn [CA]1-4, subiculum)
-Trisynaptic circuit-primary internal connections (entorhinal cortex–>dentate granule cells [synapse 1] –> CA3 via mossy fibers [synapse 2] –>CA1 via Schaffer collaterals [synapse 3]
CA1 neurons project to the subiculum (direct source to Hippocamal efferent projections
Subiculum projects back to the entorhinal cortex - completing the circuit
Neuroanatomy of Memory: Temporal Lobe Structures
Parahippocampal region
rhinal (entorhinal and perirhinal) cortex, pre- and parasubicular cortex, and parahippocampal cortex
-the perirhinal cortex and parahippocampal cortex receive a majority of the cortical input to the temporal lobe memory circuit
Two Views about the downstream medial temporal lobe pathway
- These two streams (perirhinal cortex - receives more anterior temporal ‘non-spatial info) (parahippocampal cortex receives more posteriro medial ‘spatial’ info) provide separate inputs to the hippocampus which then binds together to form an episode
- Recent findings suggest that input from the parahippocampal corte to the perirhinal cortex also presents ‘spatial’ and ‘non spatial’ cortical connections to both the perirhinal and parahippocampal cortices - allows both structures to access nonspatial and spatial information from the cortex prior to their interaction with the hippocampus
Entorhinal Cortex divided into two parts:
Anterior-lateral- receives the majority of inputs from the perirhinal cortex and ‘non spatial’ cortical regions
Posterior-medial (medial entorhinal cortex)- receives the majority of its inputs fro mthe parahippocampal cortex and “spatial’ cortical regions (this is due to grid cells - which encode spatial location in the environment and comm. with place cells of the hipp)
Network Model for Memory
complex and dense reciprocal interconnections between the many structures belonging to the temporal lobe memory system suggest that non-spatial and spatial info co-mingles prior to reacing the hipp, which may better explain the function of these structures in daily memory encoding.
3 main subcortical projections from the Hipp to structures outside the temporal lobe memory circuit
- fibers from CA1, CA3 and the subiculum project in the precommissural fornix to the lateral septal nucleus
- subicular projections travel in the postcommissural fornix and terminate on the mammillary bodies or the anterior nucleus of the thalamus
- the hipp also projects to the amygdala, nucleus accumbens, other regions of the basel forebrain, and centromedial hypothalamus
Components of Papez Circuit
hippocampal->postcommissural fornix–>mammillary body
-explains how the hypothalamus and cortex coordiante emotion-cognition interaction
Medial limbic circuit
involves projections from the mamillary bodies to the anterior thalamic nucleus and subsequent thalamic projections to the cingulate gyrus and cingulate projections, via the cingulate bundle or cingulum, which extend back to the hipp.
