Marino goes on to explain how the chronic removal of choice — which is the defining feature of captivity, no matter how large the enclosure — can lead to learned helplessness.
Many people do not attempt to imagine what it would be like to spend their entire lifetimes within one small area, with no ability to make any meaningful choices about their own lives and surroundings.

Brain damage doesn’t only happen when someone gets a bump on the
head. Research is increasingly showing that the effects of captivity
are so detrimental to animals that it’s harming their brains in much
the same way — especially in larger mammals such as dolphins and
whales.
Dr. Lori Marino, president of the Whale Sanctuary Project, writes
about the ways that captivity can cause physical changes to brain
structures, which can alter health and behavior. The cerebral
cortex, associated with functions such as cognition, memory, and
planning, can become thinner in captivity. Tiny blood vessels called
capillaries, which deliver blood to the brain, can shrink, as can
neurons. Some of these changes can be the result of enclosures that
don’t permit enough exercise, since working out can increase the
flow of oxygen to the brain and increase cognitive abilities. But
enclosures that cause boredom through a lack of stimulation can also
have similar effects.
Marino goes on to explain how the chronic removal of choice — which
is the defining feature of captivity, no matter how large the
enclosure — can lead to learned helplessness, which in turn affects
the areas of the brain responsible for processing emotions and
memory. Stereotypic behaviors, such as the endless gnawing of bars
and grates that can damage or break teeth as seen in some orcas, are
the result of an imbalance between neurotransmitters.
Unfortunately, many people still support captivity, paying money to
swim with dolphins or watch them jump through hoops. The problem is
not only a lack of information on what captivity can do to the brain
— it also stems from a lack of empathy. Many people do not attempt
to imagine what it would be like to spend their entire lifetimes
within one small area, with no ability to make any meaningful
choices about their own lives and surroundings.