Functional Neuroanatomy

Question 1

What is the 2-streams hypothesis?

Answer 1

Describes 2 qualitatively different cognitive systems that stream sensory input into perceptual and production systems.

Question 2

What is the dorsal stream?

Answer 2

Dorsal system refers to the “top” of the brain above the Sylvian fissure. Connects the occipital and parietal lobes via the superior temporal sulcus.

The dorsal system is concerned with processing and storage of SPATIAL INFORMATION, such as where something is located in space or event sequence. This is likely involved in visuomotor interaction (e.g., reaching for objects) in the environment. The dorsal stream may be more susceptible to AD changes versus the ventral stream. DORSAL LESIONS CAN PRODUCE HEMISPATIAL NEGLECT AND IMPAIRED VISUAL REACHING.

Question 3

What is the ventral stream?

Answer 3

Ventral stream refers to the “bottom” of the brain, connecting the occipital and temporal lobes. The ventral portion of the posterior cortex extracts object information, such as shape, color, and identity, and helps with facial recognition. Processes STRUCTURAL AND FEATURE-BASED INFORMATION.

This top-bottom organization is carried forward into the action system of the frontal lobe: the dorsal frontal zone determines how action is carried out.

The ventral frontal lobes make decisions about causal relations between objects and actions, but do not carry out actions.

DAMAGE TO VENTRAL STREAM CAN LEAD TO AGNOSIAS.

Question 4

What are the 3 main components of the brain?

Answer 4

1. Forebrain (cerebral hemispheres and diencephalon [thalamus and hypothalamus),
2. Midbrain (top of brainstem - tectum [colliculi] and tegmentum)
3. Hindbrain (brainstem - medulla, pons, and cerebellum)

Question 5

What is the role of the midbrain?

Answer 5

Serves roles in motor movement, particularly eye movements

Question 6

Coronal plane

Answer 6

Perpendicular to the floor, cuts across the brain between the ears

Question 7

Horizontal (or axial) plane

Answer 7

Plane that is parallel to the floor

Question 8

Sagittal plane

Answer 8

Plane from forehead to occiput (archer shooting arrow with a bow)

Question 9

Name 3 frontal lobe subdivisions

Answer 9

1. Orbitofrontal/ventromedial
2. Dorsolateral
3. Dorsomedial

Question 10

What is the role of the orbitofrontal/ventromedial area?

If there was damage in these areas, what would this look like?

Answer 10

Emotional regulation, reward monitoring, and personality.
Damage to the orbitofrontal area produces disinhibition.
Damage to the ventromedial area results in disordered reward/punishment processing and problems making decisions with reward value and emotional significance

Question 11

What is the role of the dorsolateral frontal area?

If there was damage here, what would this look like?

Answer 11

Important in a broad range of cognitive-executive functions, including working memory.

Damage to this area produces dysexecutive syndromes and impairments in working memory

Question 12

What is the role of the dorsomedial frontal area?

If there was damage here, what would this look like?

Answer 12

Important for intentional and behavioral activation.

Damage to this area produces impairment in initiated behavior including akinetic mutism, in which the person is alert and awake, but cannot move or speak

Question 13

What is the role of the temporal polar cortical area?

Answer 13

Important for intersensory integration and semantic memory.

Question 14

What is the role of the ventral temporal area?

Answer 14

Important for object recognition and discrimination; bilateral damage can produce object or face agnosia.

Question 15

What is the role of the posterior temporal area?

Answer 15

Comprised of the middle and superior temporal sulci, which contains the primary auditory areas and Wernicke’s area in the language-dominant hemisphere. Important for language comprehension.

Question 16

What is the role of the superior parietal lobe?

Answer 16

Important for sensory-motor integration, body schema, and spatial processing.

Question 17

What is the role of the temporoparietal junction?

Answer 17

Important for phonological and sound-based processing; language comprehension (left) and music comprehension (right)

Question 18

What is the role of the inferior parietal lobe?

Answer 18

This is likely in the dorsal stream. Important for complex spatial attention, integration of tactile sensation, and self-awareness.

Question 19

How many Brodmann areas are there?

Answer 19

52, although some are only in monkeys (not humans)

Question 20

The optic nerve projects posteriorly, and come together at the optic chiasm. Where do the majority of optic tract fibers terminate, from there?

Answer 20

Lateral geniculate nucleus of the thalamus, which then projects to the primary visual cortex in the occipital pole. This is called the geniculostriate pathway and is critical to visual discrimination and form perception.

A small proportion of fibers bypass the LGN and terminate in the pretectal area and superior colliculus, which then project to parietal and frontal association cortices (overall helps direct eye movements, orient to visual stimuli)

Question 21

Describe hippocampal cortical connections

Answer 21

Most hippocampal cortical connections are with the adjacent parahippocampal region, which includes the entorhinal and perirhinal cortex, pre- and parasubicular cortex, and parahippocampal cortex. The parahippocampal region is hierarchically organized, with the entorhinal cortex being the final pathway to the hippocampus. The entorhinal cortex receives afferents from the perirhinal cortex and the parahippocampal gyrus. These regions, in turn, receive projections from the unimodal and heteromodal association cortex. Thus, perirhinal and parahippocampal cortices receive majority of input from different cortical regions.

Question 22

What does the hippocampus project to?

Answer 22

Fornix to the mammillary bodies

Question 23

What does the amygdala project to?

Answer 23

Ventral amydalofugal pathway - to dorsomedial thalamus

Question 24

Who is credited for understanding neuroanatomy of memory, based on surgical resections?

Answer 24

Scoville and Milner in the 1950s. They found that removal of the amygdala caused no memory loss in one patient. in another patient, more posterior resection involving the hippocampus and parahippocampal gyrus produced amnesia. They concluded that amnesia would not occur unless resection extended far back enough to involve the hippocampus.

Question 25

What is the 2 system theory of amnesia?

Answer 25

Amnesia occurs when both the hippocampally based medial limbic circuit and the amygdala based lateral limbic circuit are damaged.

The medial/Papez circuit involves the hippocampus to mammillary bodies to anterior thalamus, to cingulate gyrus, back to hippocampus.

The lateral circuit involves the amygdala to dorsomedial thalamus to orbitofrontal lobe back to amygdala

Lesions that interrupt both the fornix and ventral amygdalofugal pathways cause severe amnesia, where lesions restricted to either pathway alone cause less severe memory disturbance.

Question 26

Which thalamic areas are important for memory?

Answer 26

Severe amnesia occurs when BOTH anterior and posterior medial thalamic areas are involved. If either of these areas are damaged alone, little memory disturbance is observed.

Thalamic amnesia may also occur with lesions affecting the internal medullary lamina (IML), which is a system of myelinated fiber tracks separating the thalamic nuclear groups (into ventral-dorsal and anterior-posterior planes).
Thalamic amnesia also occurs with lesions affecting the mammillothalamic tract.

The midline thalamic nuclei have connections with the hippocampus and are consistently damaged in patients with Wernicke-Korsakoff disease. Aside from impairing connections to the hippocampus, thalamic lesions may disconnect thalamic connections with the frontal lobes. It has been proposed that restricted thalamic lesions in Wernicke-Korsakoff disease might disconnect dorsomedial-frontal connections important for imposing cognitve structure on semantic memories residing in the posterior cortex.

Question 27

What is the role of the basal forebrain?

Answer 27

In addition to the hippocampus/temporal lobe and thalamus, it is the 3rd most essential area for memory functions. The basal forebrain is at the junction of the diencephalon and the cerebral hemispheres - reflecting a group of structures located in the vicinity of the ventromedial frontal lobes. It is comprised of the nucleus basalis, diagnonal band of Broca, substantia innominata, and medial septal nuclei. It is the major source of cholinergic input throughout the brain.

Some patients develop memory loss after hemorrhage from aneurysms of the anterior communicating artery, and it is now thought that damage to cholinergic neurons in the basal forebrain (which project to the medial and lateral limbic circuits) may be responsible. Damage to the basal forebrain is associated with profound memory loss with confabulation.

Question 28

How is language distributed in RH and LH?

Answer 28

Left hemisphere is dominant for language in more than 95% of right handers and in more than 60-70% of left handers.

Question 29

What is Wernicke’s aphasia?

Answer 29

Damage to Wernicke’s area (posterior half of the superior temporal gyrus). Primary deficit is impaired representation of the sound structure of words. Leads to reduced auditory comprehension with fluent speech (as motor-articulatory areas are intact in frontal lobe). May have poor repetition, naming, as well as right homonymous hemianopia (2/2 geniculostriate white matter damage). Considered to be a fluent aphasia.

Question 30

What is Broca’s aphasa?

Answer 30

Damage to Broca’s area (posterior aspect of the inferior frontal lobe). Primary deficit is impaired speech planning and production. Leads to reduced speech production, halting speech, and often right hemiparesis. Considered to be a non-fluent aphasia.

Question 31

What is conduction aphasia?

Answer 31

Repetition of language requires that the phonological representations generated by processing in the Wernicke’s area be converted to motor-articulatory sequences in Broca’s area. The 2 regions are connected by a large subcortical white matter pathway, the arcuate fasciculus, which is volumetrically larger in the left hemisphere than the right. Damage to the arcuate fasciculus produces a deficit in repetition with relative sparing of comprehension and fluency, a syndrom known as conduction aphasia. In addition to repetition problems there are problems with spontaneous speech

Question 32

Anomic aphasia

Answer 32

Primary deficit is impaired storage or access to lexicon. Observed symptom is problem in producing single words. Repetition and comprehension are intact. Consequence of lesion in inferior parietal lobe or connections within perisylvian language areas (many other aphasias evolve to anomia in recovery)

Question 33

What is transcortical MOTOR aphasia?

Answer 33

Primary deficit is disconnection between word/sentence representations in perisylvian region and motor speech areas. Observed symptoms include poor spontaneous speech (similar to Broca’s) with relatively perserved repetition and comprehension. Consequence of lesion to deep white matter tracks connecting Broca’s area to parietal lobe, usually caused by anterior watershed infarcts.

Question 34

What is transcortical SENSORY aphasia?

Answer 34

Primary deficit is disturbed activation of word meanings despite normal recognition of auditorily presented words. Observed symptom is disturbance in word comprehension with relatively intact repetition. Consequence of lesion to white matter tracks connecting parietal and temporal lobe; usually caused by posterior watershed infarcts.

Question 35

What is alexia without agraphia?

Answer 35

Inability to read in the context of spared writing skills. It is classic example of disconnection (Geschwind). Other examples of disconnection are optic aphasia (cannot name a visually apprehended object but can demonstrate its use) and impaired naming of objects in the left hand due to callosal disconnection of the right hemisphere from left hemisphere language areas.

Alexia without agraphia may occur following large stroke in left posterior cerebral artery. In these cases, the damaged area involves the left visual cortex, thus producing a right homonymous hemianopia, and extended anteriorly to affect interhemispheric crossing fibers in the splenium of the corpus callosum. These lesions prevent information that was appropriately perceived in the right hemisphere/left visual filed from accessing the perisylvian language areas in the left hemipshere. This then produces alexia without agraphia.

Question 36

Do the frontal lobes have strong connections with other lobes?

Answer 36

Yes. The frontal regions participate in strong cortico-cortical networks, interacting with parietal lobe systems involved in attention, propioception, and visuomotor interaction with the environment, and with the temporal lobe memory and emotional systems. Such interactions allow modulation and volitional control to be exerted on perceptual, emotional, and action systems.
Of note, the frontal lobes also have extensive cortical-subcortical connections involved in behavioral activation and selection. Giving rise to “cortical-striatal-pallidal-thalamo-cortical loops.” Cortex -> Striatum (caudate, putamen) -> globus pallidus -> thalamus. different parts of the cortex in play a role in these loops. for example when orbitofrontal cortex is the cortical input, this loop is important for response-reward learning. when anterior cingulate/limbic cortex is in the loop, it is important for emotion regulation. when dorsolateral prefrontal is the cortical input, this loop is important for executive functions.

Question 37

What is acetylcholine?

Answer 37

Plays a role in memory. Cholinergic neurons are found primarily in the pontomesencephalic region and the basal forebrain.
In the CNS, acetylcholine facilitates cortical activity subserving attention, memory, and other cognitive processes.
Muscarinic acetylcholine-containing receptors mediate the cognitive aspects (attention, learning, memory).
Nicotinic receptors are associated with neuromuscular transmission.
Drugs with strong anticholinergic properties (e.g., antihistamines, antipsychotics, and tricyclic antidepressants) may exert negative effects on cognitive performance.

Question 38

What is norepinephrine?

Answer 38

Plays a role in modulating sleep-wake cycles, attention, mood, and pain. Has an established role in mood disorders, anxiety, and OCD.

Question 39

What is serotonin?

Answer 39

Plays a role in anxiety, depression, OCD, aggressive behavior, and eating disorders.

Question 40

Where are dopamine pathways?

Answer 40

Dopamine containing neurons exist primarily in the substantia nigra. Pathways from the substantia nigra to striatum (caudate and putamen) is implicated in Parkinson’s disease.

Overactivity in other dopamine pathways may have implications for reward activity and addictive behaviors - and may result in positive symptoms of schizophrenia (delusions and hallucinations).

Question 41

Describe unimodal and heteromodal cortices

Answer 41

Unimodal cortex is devoted to processing information within a specific sensory modality (vision, audition, tactile). Unimodal association cortices are located adjacent to primary sensory areas eventually project to regions of cortex that integrate information from multiple modalities, enabling more complex modes of thought including semantic processing. These convergence regions are referred to as heteromodal because the nature of their processing utilizes and develops representation that go beyond simple sensory input channels.