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Spatial summation combines inputs arriving at different synapses. Location matters because a dendrite has axial electrical resistance and leaky membrane capacitance: a local synaptic potential need not arrive at the soma with its original amplitude or time course. A passive dendritic cable makes this attenuation explicit. The superposition principle applies to fixed electric current inputs in a linear passive model, but adding synaptic conductances changes the model's coefficients. Compare voltage changes relative to the same baseline, rather than adding absolute membrane potentials.

A motivating experiment. A 2004 study used $300$–$350\mu \mathrm{m}$ cortical slices from $18$–$28$-day-old rats at $35$–$36{}^{\circ }\mathrm{C}$. Somatic whole-cell recordings measured EPSPs in layer-5 pyramidal neurons. Two fine stimulating electrodes were positioned beside imaged dendrites; calcium-sensitive dye localized activation. Each site was stimulated alone, then both together, usually with paired pulses $20\mathrm{ms}$ apart. Comparing the combined voltage trace with the sum of individual changes tested the summation rule. Nearby inputs on one branch showed strong amplification at intermediate strengths; inputs on different branches were approximately linear.^[ref]

Blocking both excitatory receptor classes eliminated voltage and calcium responses, checking against direct electrical activation. NMDA receptor blockers eliminated or markedly reduced amplification; comparisons with inhibition intact and blocked addressed inhibitory contributions. These controls support local active integration. Passing axons could still recruit unintended synapses; somatic voltage does not measure every local membrane potential. The study tested subthreshold slice responses and pairs of branches, not arbitrary activity in an intact brain.^[ref]

A disorder of speech fluency involving disruptions such as repetitions, prolongations or blocks. Proposed timing and motor-control mechanisms must account for variability across conditions and development; brain differences measured after onset can include consequences or compensation.

The telencephalon is the anterior subdivision of the embryonic forebrain and the corresponding territory of the mature brain. Its derivatives include the cerebral hemispheres, with cerebral cortex, deeper basal ganglia and associated structures, including the olfactory bulbs. It is an anatomical and developmental division, rather than a name for one behavior or one type of neuron.^[ref]

The forebrain divides into telencephalon and diencephalon. These names should not be treated as interchangeable: the thalamus belongs to the diencephalon, whereas cerebral cortex belongs to the telencephalon. The large cerebral hemispheres can cover deeper regions in a surface view, so apparent position in a photograph alone is a poor guide to developmental membership.^[ref]

A practical example is classifying structures in a section through the brain. A region of cerebral cortex and a deep basal ganglia nucleus can both be telencephalic even though one is superficial and the other deep. Conversely, an adjacent thalamus is diencephalic. This distinction makes the telencephalon useful as a map of related structures without assuming that everything within that map performs the same computation.

Primary publication: doi.org/10.1016/S0166-4328(99)00044-3

Original article or primary record: pubmed.ncbi.nlm.nih.gov/10513581/

Behavioural Brain Research 103, 123–133; original relational account, organization and flexible expression.

Traumatic brain injury is disruption of brain structure or function caused by an external mechanical force. The damage can be focal, distributed or a combination, and its effects need not be captured by the appearance of the external head injury.

Concussion is one clinical form. Distinguishing immediate symptoms from later structural or functional findings helps avoid treating all traumatic injuries as the same mechanism or assuming that loss of consciousness is required.^[ref]

Case series of 97 right-brain-damaged patients distinguishing anosognosia, elementary deficits and neglect.

The ventricular system is the connected set of fluid-filled cavities within the brain, continuous caudally with the central canal of the spinal cord. Cerebrospinal fluid passes between ventricular compartments and the surrounding subarachnoid spaces through defined openings.