Final answer:
The largest, uppermost portion of the brain is the cerebrum, which includes the highly folded cerebral cortex and is responsible for advanced intellectual functions.
Step-by-step explanation:
The largest, uppermost portion of the brain is known as the cerebrum. This critical part of the brain is responsible for conscious, intellectual functions such as reasoning, language, memory, sight, touch, and hearing. The cerebrum's outer layer is the cerebral cortex, characterized by folds known as gyri and grooves called sulci. The cerebrum is divided into two hemispheres, the left and right, by the longitudinal fissure. The two hemispheres are interconnected by the corpus callosum, which allows communication between them. The cerebral cortex itself is a significant part of the forebrain, which also includes subcortical structures like the thalamus and hypothalamus, contributing to its status as the largest part of the brain. Moreover, the neocortex, a section of the cerebral cortex, is particularly developed in humans, accounting for a substantial portion of the brain's mass and is associated with high-level processes such as consciousness, thought, emotion, and memory.