But what exactly is the neocerebellum doing?

Both structures together are called the neocerebellum.

The same motor areas were still active because people were speaking the words, she said, but to everyone's surprise the right neocerebellum suddenly lit up.

Dr. Thach said that he believes the neocerebellum is still somehow tied to movement.

The lateral zone, which in humans is by far the largest part, constitutes the cerebrocerebellum, also known as neocerebellum.

Moreover, brain-imaging studies show that the neocerebellum is activated only when semantic reasoning is required.

The researchers found that in monkeys the primitive neocerebellum connects to a frontal region involved in planning the order and timing of future behavior.

The finding suggests that the much larger human neocerebellum might have similar, perhaps more extensive connections, Dr. Strick said.

It is sometimes equated to the "neocerebellum", since phylogenetically it is the newest part of the cerebellum.

Perhaps the neocerebellum sends its projections not to the motor cortex, as do the older parts of the cerebellum, but directly to the frontal cortex.

In mammals, the neocerebellum is the major part of the cerebellum by mass, but, in other vertebrates, it is typically the spinocerebellum.

The cerebellum of mammals contains a large portion (the neocerebellum) dedicated to supporting the cerebral cortex, which has no counterpart in other vertebrates.

If the neocerebellum and frontal lobes expanded at the same time, they might together account for the development of uniquely human traits, Dr. Leiner said.

Dr. Strick said it is tempting to make such analogies, but that it is much too soon to say what the neocerebellum does for human behavior.

Facilitatory signals arrive through the ventral reticulospinal tract from Brodmann area 4, the neocerebellum and the vestibular nucleus.

The neocerebellum, a thin layer of cells atop the older brain region, evolved more recently along with the prefrontal cortex, Dr. Courchesne said.

This finding indicated that the neocerebellum was involved in language tasks that required higher thinking, not just the movements of the tongue and larynx, Dr. Fiez said.

The frontal lobes, medial temporal lobes that include part of the auditory cortex and the neocerebellum are closer to normal size, Dr. Galaburda said.

The latest study supporting Dr. Leiner's ideas is the first to demonstrate that the neocerebellum connects to the frontal cortex via the thalamus, a midbrain structure that receives signals from all over the brain.