Encodes limits, edges, and spatial boundaries.
What It Does
Space.Boundary neurons activate on spatial limits and edges: physical boundaries ('the border between France and Spain', 'the edge of the cliff'), functional limits ('the maximum load', 'the detection threshold'), and conceptual boundaries ('the line between freedom and license', 'the limits of human knowledge'). They encode the concept of a limit or edge in any spatial or abstract domain.
How It Behaves
Space.Boundary neurons show the highest mean firing magnitude of any Space sub-type, and have a strong middle-layer concentration. The high magnitude suggests that boundaries are cognitively salient — the model represents limits with particularly strong signal. They co-activate with Boolean.Binary neurons (is something inside or outside a boundary?) and Number.Magnitude neurons (how close is something to a boundary?).
Research Example
In Mistral 7B, Space.Boundary neurons fire strongly on 'the legal gray area', 'the ethical boundary', and 'the technical limit' — abstract domain limits that share the Boundary neuron signature with physical spatial limits. This cross-domain generalization explains why models can reason consistently about legal, physical, and conceptual limits using similar linguistic patterns.