Cortical re-organization can lead to enhanced participation of the unaffected hemisphere via anomalous ipsilateral corticofugal motor projections. Recent evidence suggests that this form of neural re-organization may not be efficient. Three different types of ipsilateral projections are thought to exist: 1) fast-conducting developmental ipsilateral projections that persist beyond the age at which they normally disappear; 2) slow-conducting ipsilateral tracts present in healthy subjects that become more accessible after injury; 3) fast-conducting projections that arise de novo from the ipsilateral primary motor cortex after injury to the developing brain. Each type has a distinct neurophysiologic profile that can be characterized using transcranial magnetic stimulation (TMS) and electromyography (EMG).