The plane of Synapse is not distinct from Lowiras. In fact, Lowiras has two sides: The Sarkic (or material) side of Lowiras is the clear side, visible to all, known as Lowiras Sarkos. Synapse is the Ousic (mental) side of Lowiras, or Lowiras Ousos. Synapse is the host to the minds of every Lowiran. Their mind changes anchors throughout their Synaptic development. First, their mind is anchored to the brain they entered the world with, at the psychic level; next, their brain is hosted in the Dark Core, at the pneumatic level; finally, they abandon a physical brain as their mind is self-sustaining in Synapse, at the gnostic level. Synapse is the source of power for Lowirans, as the plane for Neuromancy, their form--and the most popular form--of Congruent Thaumaturgy.
Structure
A mind in Synapse takes up 'space' as it gains skill in Neuromancy. All space in Synapse is taken up by every mind. When a new mind is created, or a mind gains skill, Synapse simply grows in conceptual mass.
Walls between minds are easily controllable. For example, the 8 Ascendants have next to no walls between their minds as they let concepts pass freely, and they do not close themselves off from others. Though they have not the will to directly act in the Sarkic world, they provide guidance and use their power to create many microcosmic worlds for others to spend time in. Other gnostics often fill similar, though lesser roles in Synapse.
The ego, the self, can be preserved while still sharing part of one's mind in Synapse. This allows for multiple people to enter a shared mental space while preserving their individuality and privacy as much as they choose.
Tiers
Synapse is tiered by consciousness. Minds tend to connect to other minds in their tier, but Oneironauts can connect to Oneiric minds while conscious, and Hypnonauts can connect to unconscious minds.
The Conscious
The Conscious is where wakeful and aware minds dwell. Minds in the conscious are in full control of themselves. Fully in control, but also susceptible to becoming weary or bored. The focus and clarity of the Conscious are favored by pneumatics who have decent Ousic control while retaining motivation.
The Oneiric
The Oneiric is the realm of dreams, between Conscious and Unconscious. Minds have varying levels of control while dreaming. Lucid dreamers and even Oneironauts do not have full control of themselves. Dreaming can be enriching and enjoyable, and loss of control can grant more fluid thinking to the dreamer. Dreams can be shared, though establishing a connection is much more difficult, and preservation of ego becomes unreliable.
Nightmares are the ultimate loss of control in the Oneiric. The base emotions of terror and horror control the dream, causing a dreadful experience.
Dreams can degrade the ego, so prolonged dreaming can lead to madness. The Oneiric is favored by Psychics, who cannot fully perceive Synapse in consciousness.
The Unconscious
The Unconscious allows for minds to forgo control in order to regain their energy and focus. Even a damaged ego can be partially healed by enough rest. The ego is inactive in the Unconscious, so preservation is unnecessary. Connections are made passively and naturally. Subconscious ideas naturally propagate, leading to a more defined collective unconscious compared to non-Lowirans.
If a mind is weary or damaged enough, it may remain dormant until awakened by a Hypnonaut.