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Below is a coronal section from a rat brain (-2.12 Bregma). If the rat were still alive, you'd be looking into its eyes. My intention is that those interested in, and just beginning to learn about, rat neuroanatomy (and even human neuroanatomy) can print this page (try landscape if the page gets cut-off in portrait mode) and use it as a study aid. Click here for a more printer-friendly version. The goal is for you to be able to cover the left side of the picture and be able to name and describe the function of each of the outlined areas within a minutes' time. I've listed answers below (most adapted from various textbooks, compiled and translated [as best I could] into laymen terms for your convenience), with the functions generally referring to humans, though of course, analagous functions may often exist for rats as well. Keep in mind the rat brain is positioned on the horizontal plane, more so than humans. Furthermore, our neocortex is much more developed.

The Rat Brain In Stereotaxic Coordinates by Paxinos and Watson [6] is an excellent resource for learning rat brain anatomy. Its pictures and corresponding graphs are extremely detailed. However, it doesn't provide the user with their functional significance, much of which is still being elucidated. To this end, I would recommend Principles of Neural Science by Kandel, Schwartz, and Jessell [4]; The Human Nervous System: An Anatomical Viewpoint by Kiernan []; The Human Brain and Spinal Cord: Functional Neuroanatomy and Dissection Guide by Heimer []; Textbook of Clinical Neurology by Goetz []; and Adams and Victor's Principles of Neurology by Victor and Ropper [9].

Photo adapted from The Rat Brain In Stereotaxic Coordinates by Paxinos and Watson 4th ed. [6]

1. RETROSPLENIAL GRANULAR CORTEX – in humans, narrow isthmus below splenium of corpus callosum connecting cingulate and parahippocampal gyri which form limbic lobe (of Broca). Thus, part of the limbic system which involves neural circuitry important for learning, remembering, reproductive and defensive behavior, and responses to subjective feeling. [5]

2. PRIMARY SOMATOSENSORY CORTEX (SI) – spino- and trigeminothalamic afferents travel within medial lemniscus to ventral posterolateral thalamic (VPL) nucleus before projecting to area 3b where in humans, cutaneous sensation ends preferentially in anterior part and deep sensibility such as proprioception in posterior part. Occupies the postcentral gyrus on the lateral surface of the hemisphere and posterior part of the paracentral lobule on the medial surface. Consists of Brodman’s areas 1, 2 and 3. Electrical stimulation results in tingling sensation. Some extent of functional overlap with motor area of precentral gyrus. Contralateral half of body represented as inverted with pharyngeal region, mouth, tongue, and jaws most lateral, followed by the face, hand, arm, trunk, and thigh medially, and the remainder of the leg and perineum in the cortex on the medial surface of the hemispheres. []

3. SECONDARY SOMATOSENSORY CORTEX (S-II) – input from intralaminar nuclei (with reticular formation input), and posterior thalamic nuclei (with spino- and trigeminothalamic input), and from four areas of S-I, and projects to insular cx which innervates rgns of temporal lobe important for tactile memory, and involved mainly in less discriminative aspects of sensation. In the dorsal wall of the lateral sulcus adjacent to the postcentral gyrus and may extend onto the insula. Bilateral representation exists though contralateral representation predominates. []

4. CORPUS CALLOSUM – composed of most of the neocortical commissural fibers (about 300 million in humans) which connects corresponding areas of one hemisphere with the other. Largest bundle of fibers in the brain, joins the two cerebral hemispheres. []

5. ANTERODORSAL THALAMIC NUCLEUS – gateway between thalamus and frontal lobes, may imbue cognitive aspects of sensory processing with emotive overtone, part of limbic system. Dark-staining cells at the rostrodorsal pole of thalamus. Located more medially and rostrally than anteroventral nucleus and associated with limbic system. []

6. ANTEROVENTRAL THALAMIC NUCLEUS – subcortical afferents received from pallidum then projects to extensive areas of frontal lobe, including premotor and supplementary motor areas and frontal eye field. Located lateral to, and more caudally than, anterodorsal nucleus and associated with more recently evolved special sensory systems. []

7. RETICULAR THALAMIC NUCLEUS – not affiliated with reticular formation, has very unusual functional organization: (1) solely GABAergic, (2) projects to all thalamic sensory and motor nuclei, (3) receives broad input from thalamus, tegmentum, and cerebral cortex, and (4) controls levels of consciousness and alertness. On the perimeter of rostrolateral thalamus beside the ventrobasal complex. A long, slender shell of neurons. Part of pathway from reticular formation through intralaminar nuclei to cerebral cortex for influence of sensory input to brain stem and spinal cord on levels of consciousness and alertness. []

8. INTERNAL CAPSULE – contains axons interconnecting cerebral cortex, thalamus, and striatum (consists of caudate nucleus and putamen). Disconnection syndromes detrimental since lesioning its reciprocal connections may affect several key elements in a processing sequence. Thick band of fibers bounding the lateral surface of the diencephalon and connecting the cerebral cortex with the thalamus and other parts of the CNS. []

9. LATERAL PALLIDUM (GLOBUS PALLIDUS) – major output is inhibitory to certain thalamic nuclei, which excite premotor and supplementary motor areas of cerebral cortex, cortical areas associated with eye movements, and regions of prefrontal and temporal cortex. Along with the striatum (caudate nucleus and putamen) comprises the corpus striatum, the telencephalic gray matter associated with lateral ventricle. Other efferents inhibit the subthalamic nucleus and pedunculopontine nucleus, which projects rostrally to basal ganglia and caudally to reticular formation nuclei that send motor fibers to spinal cord. At rest, neurons in striatum are quiescent and those in pallidum are active which inhibits thalamic excitation of motor cortex. Before and during movement, striatum becomes active and inhibits pallidum allowing for more excitation of motor thalamic nuclei and cortex. []

10. REUNIENS (INTRALAMINAR) THALAMIC NUCLEUS – composed of several nuclei projecting broadly and without topography upon entire cerebral cortex for profound role in control of its excitability. Electrical stimulation results in synchronous frequency firing of cortex. Profusely branching axons, resembling aminergic groups of neurons in brain stem (eg A6). In contrast, other thalamocortical nuclei that are modality-specific do not branch as profusely, have thicker axons, and project upon cortex in topographic fashion. Input from medial cortex and hippocampus and projects widely to basal forebrain structures without much topography. []

11. MAMMILLOTHALAMIC TRACT (FASCICULUS) - allows hypothalamus to participate in acquisition and consolidation of memories, subjective feelings, and visceral manifestations of emotions through ANS. Also known as the bundle of Vicq d’Azyr, part of the limbic system, composed of rostrally directed afferents from the mamillary bodies of posterior hypothalamus to anterior thalamic nuclei. Not directly related, although interconnected, to the hippocampus. []

12. PERIVENTRICULAR NUCLEUS – strongly influences median eminence, medulla, spinal cord, and neurohypophysis. Main role is peptidergic control of neurohypophyseal system through portal circulation. Forms small, triangular wings caudal and dorsal to periventricular nuclei. One of the two principal descending pathways from the hypothalamus. Thinly myelinated and unmyelinated fibers beneath the ependyma of the third ventricle which continues into the dorsal longitudinal fasciculus in the periaqueductal gray of the midbrain. Originates mainly from the small cells of the paraventricular nucleus. Some end in the dorsal nucleus of the vagus nerve and presumably in the salivatory and lacrimal nuclei. Others continue into the spinal cord terminating in the intermediolateral cell column and sacral autonomic nucleus allowing the hypothalamus direct influence on preganglionic neurons of sympathetic and parasympathetic nervous systems. []

13. PARAVENTRICULAR NUCLEUS – along with supraoptic nucleus has plentiful supply of capillaries allowing elaboration of adeno- and neurohypophyseal hormones. Contains large cells in a matrix of smaller neurons. Cytoplasmic neurosecretory granules are evidence of neurosecretory activity. Just beneath thalamic midline nuclei. Amazingly complex neurochemical anatomy having roles in ovulation, milk ejection reflexes, parturition, gut motility, descending control of pain, regulation of drinking, growth hormone secretion, etc. with these pathways forming three groups: those (1) innervating neurohypophysis through release of peptides into inferior hypophyseal artery in infundibulum, (2) projecting to median eminence of adenohypophysis and either conventionally synapsing on peptidergic neurons or directly releasing neuroactive peptides into superior hypophyseal artery, and (3) influencing ANS principally through oxytocin secretion/release. []

14. FORNIX – fiber bundle carrying portion of outflow of hippocampus, projecting dorsally through cerebral peduncles, passing through tectum, around thalamus, projecting mainly to mammillary bodies. []

15. MEDIAL FOREBRAIN BUNDLE – important fiber tract conveying (1) bidirectional visceromotor and limbic-related information between septal nuclei and olfactory areas, and (2) ascending sensory input from various brain stem areas (raphe and tegmental nuclei, cranial nerve sensory and motor nuclei, and reticular formation of midbrain) to hypothalamus. Containing cells originating chiefly from septal area, with other fibers from intermediate and lateral olfactory areas. Conducts data related to basic emotional drives and sense of smell. Runs caudally in lateral zone of hypothalamus, giving off fibers to various hypothalamic nuclei. Other fibers continue through hypothalamus to raphe nuclei of reticular formation of midbrain and pons. Also contains ascending fibers originating in locus coeruleus and ventral tegmental area of brain stem terminating in hypothalamus. []

16. LATERAL HYPOTHALAMIC AREA – through connections with subfornical organ (a chemosensitive nucleus) and hypothalamus, involved in regulation of drinking behavior. Connections and functions are similar to nearby zona incerta. Contains fewer neuronal cell bodies than other hypothalamic areas, but many fibers, with most running in a longitudinal direction. Far removed from any direct role in neurosecretion. Ascending trigeminal fibers en route to the ventral posterolateral thalamic nucleus pass through this region.

17. MEDIAN EMINENCE – part of neurohypophysis that is a small lump in midline of tuber cinereum of hypothalamus containing primary capillaries of hypophyseal portal system. Gives rise to the pituitary stalk immediately behind optic chiasma which forms neurohypophysis. Small protrusion marking rostral two-third of pituitary. []

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