Functional Neuroanatomy Flashcards
Disconnection Syndrome
Damage to the white matter pathways when functional brain regions are deprived of inputs and outputs through white matter damage.
Gray matter vs White matter
Gray = cell bodies of neurons
White = mostly myelinated axons
Unimodal cortex vs Polymodal cortex
Unimodal = processes information pertaining to a specific sensory modality; primary role in perception
Polymodal =processes information received from disparate modalities through afferent connections; primary role in higher order conceptual processes
Frontal lobe cortical divisions (3)
Orbitofrontal/ventromedial region
Dorsolateral region
Dorsomedial region
Orbitofrontal/ventromedial region
emotional regulation, reward monitoring, and personality
Orbitofrontal damage may cause disinhibition
ventromedial damage may cause disordered reward/punishment processing, problems making perceptual or learning experiences with reward value and emotional significance
Dorsolateral region
broad range of cognitive-executive functions
Damage produces dysexecutive syndromes, impairments in working memory and poor attentional control of behavior
Dorsomedial region
intentional and behavioral activation
Damage produces impairments in initiated behavior (in extreme cases may cause akinetic mutism - in which person is alert and awake but cannot move or speak)
Temporal lobe cortical areas (2)
Ventral temporal area
Posterior temporal area
Ventral temporal area
object recognition and discrimination
bilateral damage can produce object or face agnosia
Posterior temporal area
contains primary auditory areas and Wernicke’s area in the language-dominant hemisphere, important for language comprehension, and prosodic comprehension in the homologous non-dominant hemisphere
Parietal lobe cortical divisions (3)
Superior parietal lobe
Temporoparietal junction
Inferior parietal lobule
Superior parietal lobe
important for sensory-motor integration, body schema, and spatial processing
Temporoparietal junction
phonological and sound-based processing; language comprehension (left) and music comprehension (right)
Inferior parietal lobule
complex spatial attention, integration of tactile sensation, and self-awareness
Occipital lobe cortical divisions (2)
Ventral visual pathway
Dorsal visual pathway
Ventral visual pathway
connects occipital and temporal lobe
important for object and face recognition, item-based memory, and complex visual discrimination
Dorsal visual pathway
connects occipital and parietal lobe via superior temporal sulcus
important for spatial vision and visuomotor integration
Concept of functional system (processors and connectors)
An interconnected group of cortical and subcortical structures that each contributes to important components of complex behavior or skill. Complex behavior, such as memory or language, can be impaired by damage to the processors themselves or by damage to their connecting fibers
damage to processer = loss of function
damage to connector = disconnection syndrome, loses full ability to coordinate or communicate
Neuroanatomy of Vision (pathway)
Retinal ganglion cells in each eye > optic nerve > optic chiasm > optic tract > lateral geniculate nucleus (LGN) of the thalamus > primary visual cortex (Brodmann 17)
From LGN, pathway called “geniculostriate”
Note. A small portion of fibers bypass the LGN and terminate in the pretectal area and superior colliculus (forming the “extrageniculate” visual pathway)
“Dorsal” and “Ventral” pathways
Dorsal = (“Where”) projects to parieto-occiptal association cortex; processes spatial information. Lesions cause impairments in spatial perception, attention, and visuomotor processing
Ventral = (“What”) projects to occipito-temporal association cortex; processes structural and feature-based information. Lesions cause impairments in perceptual disturbances, poor recognition of objects/faces (agnosias)
Apperceptive (visual) disorder
a disorder results rom impairment in processing basic visual elements of objects (e.g., shapes, contour, depth)
Associative angosia
Associative agnosia
When the recognition disorder results from relating well-perceived stimulus to stored representations based on prior experiences with the stimulus
Primary cortical inputs into the hippocampus (2)
Ventral Stream > unimodal (primarily visual) cortical areas > perirhinal cortex (PRc) -> Lateral Entorhinal cortex (L-ERc) > HC CA1 and HC CA3
Dorsal Stream > Parietal and Frontal association areas > Parahippocampal cortex (PHc) > Medial entorhinal cortex (M-ERc) > HC CA1 and HC CA3
Both end at HC CA1 and HC CA3
Neuroanatomy of Memory: Medial (Papez) circuit
Hippocampus -> postcommissural fornix -> mammillary bodies -> mammillothalamic tract -> anterior thalamic nucleus -> thalamic projections -> cingulate gyrus and cingulate bundle -> cingulate bundle or cingulum -> hippocampus
Neuroanatomy of Memory: Lateral limbic circuit
Amygdala -> dorsomedial nucleus of the thalamus -> orbitofrontal cortex -> uncinate fasciculus -> amygdala
Hippocampus structure
Consists of dentate gyrus, sectors of Ammon’s horn (cornu Ammonis [CA] 1-4), and the subiculum
The primary internal connections comprise what is known as the ‘Trisynaptic circuit’
(entorhinal cortex > dentate granule cells (synapse 1) > CA3 via mossy fibers (synapse 2) > CA1 via Schaffer collaterals (synapse 3)
Amygdala structure
two main parts: a large basolateral group of nuclei (which connect to limbic system, association cortex, and dorsomedial thalamic nucleus) and a smaller corticomedial segment (connects with basal forebrain, hypothalamus, and brainstem)
Similar anatomical connections of amygdala and hippocampus
Both 1) strongly interconnected with frontal and temporal limbic cortex, 2) have indirect polymodal neocortical association areas, 3) project to basal forebrain and hypothalamus, and 4) connect directly with each other
Anatomical Basis of Temporal Lobe Amnesia (two-system theory of amnesia)
Amnesia occurs when both the lateral and medial limbic circuits are damaged (explains most diencephalic and BF amnesias as well). Lesions that disrupt both cause severe amnesia, whereas lesions restricted to either pathway alone cause less severe memory disturbance
Four conclusions about temporal lobe and amnesia:
1) damage to cortical or subcortical structures within temporal lobe, whether focal or extensive, can result in amnesia
2) Amnesia most likely results from damage to both circuits
3) Damage to individual elements of these circuits can all result in amnesia, provided that both circuits are damaged
4) Hippocampus is critical for episodic memory, whereas amygdala critical for emotional aspect of cognition (including emotional memory)
Thalamus role in Memory
Thalamus is primarily a sensory relay nucleus but has critical functions in high cognitive processes (alertness, behavioral activation, and memory)
Thalamic amnesia best correlates with lesions affecting the internal medullar lamina (IML) and mammillothalamic tract
Basal Forebrain role in Memory
Located at the junction of the diencephalon and cerebral hemispheres (vicinity of the ventromedial fontal lobe, anterior to the caudate and putamen)
Composed of: the septal area, diagonal band of Broca, nucleus accumbens septi, olfactory tubercle, substantia innominata, bed nucleus of the stria terminals, and preoptic area.
Damage associate with profound memory loss with confabulation, the latter of which is likely associated with neighboring frontal lobe
Approx. % of left-hemisphere language dominance
95% for right-hand
60-70% for left hand
Broca’s Area
(BA 44, 45); dominant side of frontal lobe
Damage causes a Nonfluent Aphasia (expressive) with deficits in written or verbal expression (speech planning and production)
Connects with other frontal regions and appears necessary for processing syntax and grammatical structure of language
Wernicke’s Area
(BA 22) dominant side of temporal lobe
Damage to Wernicke (BA 22) and surrounding areas (BA 37, 39, and 40) causes Fluent Aphasia (receptive) with deficits in comprehension
Reciprocally connected with supramarginal and angular gyri in the parietal lobe - important for comprehension, writing, and for mapping sounds to meaning (lexical semantics); also connections with visual areas important for recognition of word forms (important for reading)
Arcuate Fasciculus
A large subcortical white matter pathway that connects Broca (BA 44, 45) and Wernicke (BA 22).
Damage produces disproportionate deficits in repetition, with relative sparing of comprehension and fluency (Conduction Aphasia)
Prosody of Language
Defined as use of tone, pitch, rhythm, and other vocal intonation patterns to convey meaning and emotion
Primarily processed in the right (non-dominant) hemisphere
Anomic Aphasia
Poor single word production (impaired storage or access to lexicon)
Damage to inferior parietal lobe or connections within perisylvian language areas
Transcortical Motor Aphasia
Disturbed spontaneous speech similar to Broca’s; relatively preserved repetition and comprehension
A disconnection between conceptual word/sentence representations
Damage to deep white matter tracts connecting BA to parietal lobe, usually caused by anterior watershed infarcts
Transcortical Sensory Aphasia
Disturbance in word comprehension (meanings) with relatively intact repetition
Damage to white matter tracts connecting parietal and temporal lobe, usually caused by posterior watershed infarcts
Frontal Lobe network of “selective engagement”
Networks in the frontal lobe allow for the flexible selection and activation of cortical regions necessary to perform cognitive work
E.g., summing up the name of a friend
Frontal-subcortical Interaction - primary loop?
Cortico-Striatal-Pallidal-Thalamo-Cortical Loop
3 interconnected systems for attention (Posner & Rothbart, 2007)
Orientation - refers to tuning of perceptual systems to incoming stimuli so that relevant information from sensory input can be selected for further processing (primarily acetylcholine)
Alerting - state of sensitivity to incoming stimuli (primarily norepinephrine)
Executive attention - involves monitoring and resolving conflicts among thoughts, feelings, and behaviors (primarily dopamine)
Key anatomic facts concerning Working Memory
1) dorsal (spatial) - ventral (object-based) distention appears to exist in the frontal working memory systems just as it does in posterior cortex
2) dorsal components of the frontal working memory system are preferentially connected to structures in the dorsal visual stream and vise-versa
Neurotransmitter & cognitive relevance: Acetylcholine
Attention, memory, regulation of thalamic output
Neurotransmitter & cognitive relevance: Norepinephrine/Noradrenaline
Attention shifting; arousal
Mood; sleep-wake cycle
Neurotransmitter & cognitive relevance: Serotonin
Mood, arousal
Pain, respiration, temperature, motor control
Neurotransmitter & cognitive relevance: Dopamine
Motor regulation; thalamic gating
Memory, reward systems
Executive function, working memory, “top-down” attention, motor initiation
Lactation, menstruation, sexual behavior
Neurotransmitter & cognitive relevance: GABA
Broad neuromodulatory functions
Neurotransmitter & cognitive relevance: Glutamate
Broad excitatory functions
