Everyone knows the myth of Medusa.
Medusa, basilisks, cockatrices, the Odalisque. Beings with the ability to kill, not by looking at someone, but when one looks at them. An interesting concept, and, if weaponized, behaves as a passive weapon, requiring precautions to be taken against them.
Instances of Medusa weapons exist in literature. Snow Crash, of its titular book, is an image of white noise which enters through the visual cortex and exploits the neural processing pathways to crash the brain. Basilisks, from David Langford's short stories, are images which crash the mind by triggering impossible thoughts.
But are Medusa weapons possible? At first glance, an image that can kill one who merely looks at it seems absurd. However, generalizing a Medusa weapon to any object that, through manipulating the senses, ceases normal cognitive function, it's possible to see certain methods by which they can occur.
The first weapon that comes to mind is the taser, which, by literally overloading the nervous system, which can lead to brain injury and even death. However, it involves an external energy source and direct contact, which make it unsuited for the definition of Medusa weapons. However, it does involuntarily shut down brain function, and other methods pain compliance may also be considered to fall within this wide and vague definition (although pain compliance has the additional support of using the victim's nervous system itself to generate the pain, rather than the electrical potential applied from an external source).
Moving slightly past the sense of touch, inhaled anaesthetics can also be used to halt normal cognitive function. Although still requiring physical contact, gases can be dispersed more easily and from a distance, obviating the need of direct physical contact. However, chemical agents cause disruption through passing through the blood-brain barrier and physically obstructing the nerve channels, which would not be fairly considered "manipulating the senses". Theoretically the sense of smell can be used to overload the brain, however, I do not believe that there have been recorded instances of anyone being "knocked off their feet" by smell.
A close candidate for an actual Medusa weapon would be the flashbang, causing blindness and disorientation for a period of time through a combination of aural and visual stimulus. However, the sensory overload does not "crash" the brain so to speak, rather, the brain requires time to recalibrate the senses after the sudden flood of stimulus. Excess auditory stimulation to the point of pain could be considered cognitive shutdown, however, the crash ends as soon as the sound ceases.
The only real-life example of a Medusa weapon would be visual patterns capable of triggering photosensitive epilepsy. Fulfilling the definition of a Medusa weapon, a static, regular pattern is capable of triggering an epileptic seizure. However, only people who are predisposed to photosensitive epilepsy, through previous brain damage or genetic abnormalities, are sensitive to such a Medusa weapon.
So can we create a general purpose Medusa weapon?
The answer is we don't know.
We currently don't have a strong enough understanding of human brain function in order to design Medusa weapons, however, I believe it can be done. The human brain wasn't designed in any conventional sense, and there is no cause to believe that the human brain is free from exploits. It has been theorized that photosensitive epilepsy is caused by synchronous neural firings which disrupt normal brain function, and although these firings are only synchronized in aberrant brains, it is not unreasonable to think that some combination of stimulus would result in erroneous firing combinations in a normal brain, resulting in brain crash. However, the variation between brains are great, and it may be difficult to find a universal exploit available in all brains.
I remain hopeful. The human brain still has many mysteries to be plumbed, and when its mechanics is finally discovered, the hackers will not be far behind.