  Transition from quasiperiodicity with many frequencies (i.e., a
high-dimensional torus) to chaos is studied by using $N$-dimensional globally
coupled circle maps. First, the existence of $N$-dimensional tori with $N\geq
2$ is confirmed while they become exponentially rare with $N$. Besides, chaos
exists even when the map is invertible, and such chaos has more null Lyapunov
exponents as $N$ increases. This unusual form of "chaos on a torus," termed
toric chaos, exhibits delocalization and slow dynamics of the first Lyapunov
vector. Fractalization of tori at the transition to chaos is also suggested.
The relevance of toric chaos to neural dynamics and turbulence is discussed in
relation to chaotic itinerancy.
