Somatosensory Disorders: Disorders of sensory information received from superficial and deep regions of the body. The somatosensory system conveys neural impulses which pertain to proprioception, tactile sensation, thermal sensation, pressure sensation, and pain. PERIPHERAL NERVOUS SYSTEM DISEASES; SPINAL CORD DISEASES; and BRAIN DISEASES may be associated with impaired or abnormal somatic sensation.Evoked Potentials, Somatosensory: The electric response evoked in the CEREBRAL CORTEX by stimulation along AFFERENT PATHWAYS from PERIPHERAL NERVES to CEREBRUM.Somatosensory Cortex: Area of the parietal lobe concerned with receiving sensations such as movement, pain, pressure, position, temperature, touch, and vibration. It lies posterior to the central sulcus.Touch: Sensation of making physical contact with objects, animate or inanimate. Tactile stimuli are detected by MECHANORECEPTORS in the skin and mucous membranes.Vibrissae: Stiff hairs projecting from the face around the nose of most mammals, acting as touch receptors.Physical Stimulation: Act of eliciting a response from a person or organism through physical contact.Touch Perception: The process by which the nature and meaning of tactile stimuli are recognized and interpreted by the brain, such as realizing the characteristics or name of an object being touched.Bipolar Disorder: A major affective disorder marked by severe mood swings (manic or major depressive episodes) and a tendency to remission and recurrence.Median Nerve: A major nerve of the upper extremity. In humans, the fibers of the median nerve originate in the lower cervical and upper thoracic spinal cord (usually C6 to T1), travel via the brachial plexus, and supply sensory and motor innervation to parts of the forearm and hand.Afferent Pathways: Nerve structures through which impulses are conducted from a peripheral part toward a nerve center.Thalamus: Paired bodies containing mostly GRAY MATTER and forming part of the lateral wall of the THIRD VENTRICLE of the brain.Brain Mapping: Imaging techniques used to colocalize sites of brain functions or physiological activity with brain structures.Mental Disorders: Psychiatric illness or diseases manifested by breakdowns in the adaptational process expressed primarily as abnormalities of thought, feeling, and behavior producing either distress or impairment of function.Anxiety Disorders: Persistent and disabling ANXIETY.Mood Disorders: Those disorders that have a disturbance in mood as their predominant feature.Ventral Thalamic Nuclei: A large group of nuclei lying between the internal medullary lamina and the INTERNAL CAPSULE. It includes the ventral anterior, ventral lateral, and ventral posterior nuclei.Electric Stimulation: Use of electric potential or currents to elicit biological responses.Neural Pathways: Neural tracts connecting one part of the nervous system with another.Sensation: The process in which specialized SENSORY RECEPTOR CELLS transduce peripheral stimuli (physical or chemical) into NERVE IMPULSES which are then transmitted to the various sensory centers in the CENTRAL NERVOUS SYSTEM.Forelimb: A front limb of a quadruped. (The Random House College Dictionary, 1980)Diagnostic and Statistical Manual of Mental Disorders: Categorical classification of MENTAL DISORDERS based on criteria sets with defining features. It is produced by the American Psychiatric Association. (DSM-IV, page xxii)Thalamic Nuclei: Several groups of nuclei in the thalamus that serve as the major relay centers for sensory impulses in the brain.Magnetoencephalography: The measurement of magnetic fields over the head generated by electric currents in the brain. As in any electrical conductor, electric fields in the brain are accompanied by orthogonal magnetic fields. The measurement of these fields provides information about the localization of brain activity which is complementary to that provided by ELECTROENCEPHALOGRAPHY. Magnetoencephalography may be used alone or together with electroencephalography, for measurement of spontaneous or evoked activity, and for research or clinical purposes.Cerebral Cortex: The thin layer of GRAY MATTER on the surface of the CEREBRAL HEMISPHERES that develops from the TELENCEPHALON and folds into gyri and sulchi. It reaches its highest development in humans and is responsible for intellectual faculties and higher mental functions.Reaction Time: The time from the onset of a stimulus until a response is observed.Magnetic Resonance Imaging: Non-invasive method of demonstrating internal anatomy based on the principle that atomic nuclei in a strong magnetic field absorb pulses of radiofrequency energy and emit them as radiowaves which can be reconstructed into computerized images. The concept includes proton spin tomographic techniques.Functional Laterality: Behavioral manifestations of cerebral dominance in which there is preferential use and superior functioning of either the left or the right side, as in the preferred use of the right hand or right foot.Neurons: The basic cellular units of nervous tissue. Each neuron consists of a body, an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the NERVOUS SYSTEM.Fingers: Four or five slender jointed digits in humans and primates, attached to each HAND.Proprioception: Sensory functions that transduce stimuli received by proprioceptive receptors in joints, tendons, muscles, and the INNER EAR into neural impulses to be transmitted to the CENTRAL NERVOUS SYSTEM. Proprioception provides sense of stationary positions and movements of one's body parts, and is important in maintaining KINESTHESIA and POSTURAL BALANCE.Electroencephalography: Recording of electric currents developed in the brain by means of electrodes applied to the scalp, to the surface of the brain, or placed within the substance of the brain.Tibial Nerve: The medial terminal branch of the sciatic nerve. The tibial nerve fibers originate in lumbar and sacral spinal segments (L4 to S2). They supply motor and sensory innervation to parts of the calf and foot.Neuronal Plasticity: The capacity of the NERVOUS SYSTEM to change its reactivity as the result of successive activations.Hand: The distal part of the arm beyond the wrist in humans and primates, that includes the palm, fingers, and thumb.Depressive Disorder, Major: Marked depression appearing in the involution period and characterized by hallucinations, delusions, paranoia, and agitation.