Montgomeryshire AM Mick Bates may not have known what he was doing after allegedly attacking paramedics trying to treat him following a fall down a flight of stairs, a court heard.
Bates, of Llanfair Caereinion, near Welshpool, is accused of lashing out at paramedics and hospital staff after suffering a fall outside Charleston Steak House in Cardiff on January 20.
But the 63 year old claims he did not know what he was doing after suffering a bang on the head during the fall.
He denies three charges of assault and three separate public order offences.
At Cardiff Magistrates Court yesterday, where Bates is standing trial, consultant neurologist Dr Christopher Gardner-Thorpe said the contribution of alcohol to the incident would have been minimal and claimed experts could not be sure he knew what he was doing.
The alleged incidents happened at Charleston Steak House, in the back of an ambulance and at University Hospital of Wales, Cardiff.
Dr Gardner-Thorpe said neither concussion nor a lack of consciousness could be ruled out.
He said: "There are difficulties with defining consciousness and concussion, but we cannot exclude the issue of concussion and we cannot be certain that he was acting with full consciousness following the fall.
"It is possible that Bates was not acting in full consciousness and therefore not making a proper judgement of his actions. Head injuries have a lot of subtle effects and change behaviour in ways not obvious by physical examination."
When asked if the evidence he heard led him to think that Bates had suffered a "significant head injury", he replied "yes".
Earlier, the court heard Bates did not seem excessively drunk or unsteady on his feet in the hours before the alleged attacks.
Eryl Vaughan, managing director of the Wales Energy Company, said he had shared two bottles of wine with Bates and left him at about midnight.
"He came outside to see me into a taxi and seemed fine," said Mr Vaughan. The trial continues.
By Andrew Morris