Joe Biden's fitness to run for a second term is in question after 'senior moments' during last night 'car crash' TV debate sparked a wave of concern.

The President's jumbled words and a general frail appearance put him in stark contrast to Republican hopeful Donald Trump, commentators said. 

Last night is just the latest in a string of incidents that have led many to speculate on Biden's health. His time in office has been punctuated by falls, gaffes and unusual behaviour, particularly in recent months. 

To add to his woes, there are reports that some Democrats are now calling for him to step out of the presidential contest altogether — a suggestion firmly rebutted by the Biden camp.

So can any firm conclusions be drawn on what might be wrong with the 81-year-old based on his performance? We asked one of the UK top dementia specialists, who watched the debate, for his view. 

Speech: Jumbled words, lost sentences and incoherence

In what has become a much commented on moment of the TV debate, Biden produced a rambling response to a Medicare question.

He said: 'We've been making sure we are able to make every single person eligible what I've been able to do with the Covid, excuse me, everything we have to do with...look... I finally beat Medicare...' before trailing off. 

Another serious fumble came when Biden spoke about the the situation on the US border.

'We had significant increase in number of asylum officers significantly. By the way the Border Patrol been endorsed me, endorsed my position. 

'In addition to that we find ourselves in a situation where when he was president he was taking separating babies from their mothers put him in cages,' he said 

This led to Trump to respond: 'I really don't know what he said at the end of that sentence. I don't think he knows what he said either.'

Professor Robert Howard, an expert in old age psychiatry at University College London, said: 'Doctors can't diagnose someone without examining them, but based on the footage of the debate I've watched, the freezing and rambling make me concerned that Biden struggles to maintain attention.

'He's fine 98 per cent of the time, but there are occasions when he appears to have lost his train of thoughts and others where he can't stop himself from rambling.

'These fluctuations and dips in attention are a key symptom of Parkinson's.'

Parkinson's is a condition in which nerve cells in the part of the brain responsible for producing a vital chemical called dopamine stop working properly.

Dopamine governs a range of functions including movement and attention, and while medication can help alleviate the symptoms, the illness is incurable and gradually worsens. 

Dr Mike Smith, an NHS GP from Hertfordshire, said watching last night's debate had left with only one conclusion as a health professional. 

'It is beyond doubt he has cognitive impairment,' he said. 

He escribed Biden as having telltale signs of the problem, which can be caused multiple neurological conditions.

'He struggles to find the right word, he sometimes finishes a sentence with something that makes no sense for example his sentence on Medicare… he appears to have to concentrate very had to keep on topic.

'Also his shuffling indicates there's some locomotive issues there as well.'

Memory: Trailing off, confused gaffes and freezes 

Biden's memory and ability to continue a points were also highlighted by the recent debate. 

At one moment, when singling US states restrictions on abortion, he confusingly pivoted to immigration and referred to a 'young woman who was just murdered' by an immigrant. 

Viewers claimed it was unclear what point he was trying to make. 

Other commentators have pointed to several occasions when he has seemingly frozen  such as one incident earlier this month where he was seemingly staring blankly ahead as Vice President Kamala Harris danced beside him.

But there have been plenty of times Biden has appeared disorientated and frozen in public. 

At the ceremony commemorating the 80th anniversary of D-Day in France Biden was seen awkwardly squatting down as if he was preparing to sit before momentarily freezing. 

The move seemed to prompt First Lady Jill Biden to cover her mouth – raising questions about whether she quietly tried to offer him advice that it was not the right time to sit.

He also appeared to freeze for about a minute are look vacant during the Juneteenth celebrations while others grooved along to a lively band.

There has been widespread speculation, as a result of these incidents, that the President has dementia. 

However Professor Howard said: 'People with dementia have these symptoms all the time, not intermittently.

'If you sit someone with dementia down in front of a neuropsychologist and test them, they will do badly.

'Someone with fluctuating attention will only do badly when their attention dips.'

He said this appears to be what's happening with the President.  

'It's just really bad luck that Biden seems to be affected when he's on show,' he said.

'It will also be difficult for those around him. If he had dementia, they could test him and say, look, you're not fit to carry on as President or a candidate.

'But if it's fluctuating it's only those moments that are a concern and the rest of time he'll be absolutely fine.'

While both dementia and Parkinson's can effect the brain Professor Howard said they manifest in different ways. 

'The difference is, with dementia it's like the lights in the house are blown: there's nothing you can do bring them back on,' he said. 

'But with something like Parkinson's, the power dips, and the bulbs flicker and go a bit dim from time to time. 

'Biden just has a problem keeping the lights on all the time.

'He looks expressionless and his face has a mask-like appearance. This is something we also often see with Parkinson's disease.'

He added that people shouldn't dismiss symptoms such as these as they are not simply a sign of ageing. 

'If [Biden] has Parkinson's — and I'm not saying he has — you can bet he'll have seen top doctors and will be on optimal treatment already,' he said. 

'These sorts of symptoms shouldn't be seen as a normal part of old age.'

Dr Smith added that if he was examining a patient with Biden's symptoms he would want to consider Parkinson's. 

If a relative brought Mr Biden into me at the practice and they explained all the things we witnessed in the presidential debate last night, and some of the more recent public appearances, Parkinson's would be one of the top things in the list to exclude,' he said. 

But he added that dementia or an infection, given Biden's age, would also be among the health issues that a medic would also want to consider.

Walking: General stability and multiple trips and falls   

Shaking hands is perhaps one of the most well-known symptoms of Parkinson's, but experts say not all patients develop it.    

Falls, which Biden has becoming increasingly vulnerable to, are another sign of the condition. 

The President has several unfortunate tumbles over the past few years. 

Perhaps the most iconic was when he repeatedly stumbled on the stairs while boarding Air Force One in March 2021 and then again in May 2022.

Another incident, this time in June 2022, saw Biden lie on the ground for 10 seconds after he fell from a stationary bike while talking to reporters. 

Other falls have been also filmed and recorded at various events over the past year.  

Professor Howard said falls among Parkinson's sufferers not uncommon.

'People with Parkinson's get these moments where they freeze up physically,' he said.

'They are more likely to suffer falls as the legs can be stiff and movements slow.'

The brain chemical dopamine, which Parkinson's patients have less of, acts as messenger between the brain and the parts of the nervous system that govern the control and co-ordination of body movements.

A lack of it can lead to movement becoming slow or abnormal with patients at increased risks of falls as a result, and can even cause them freeze completely as if stuck to the spot.

Parkinson's affects one in 20 people over the age of 85, with age considered the biggest risk factor for developing the disease. 

Professor Howard said while he couldn't comment on Biden's long term health, if he did have Parkinson's, he would only get worse over time as the condition was progressive. 

'It's a terrible dilemma as the majority of the time he's on point. 

'But you can't predict when these moments will happen and he won't be able to function at the level he needs to be at,' he said.

'These things do not get better as time goes on. They are progressive. Medications only treat the symptoms, they don't stop the disease from progressing. 

'Thinking ahead to the next three or four years, it will only get worse.'

Dr Smith also said the conditions that cause cognitive impairment inevitably get worse over time.

'The analogy I would use is that you have a very large bookcase where the small books are on the top and the big book are on the bottom,' he said. 

'The earlier signs of cognitive impairment and dementia are where the bookcase is being gently rocked and the small books start to fall, 'Where did I put my bank card?', 'What did I have for lunch yesterday…those types of things.' 

He add that while Biden is doubtlessly being looked after by a team of medical experts it did raise questions about his future.

'Is this gentleman who wants to do another four year term as the President of the US, is that really in his best interest? That's the question I was asking myself when I saw the debate,' he said. 

Dr Smith also said it was critical that people don't dismiss any potential signs of cognitive impairment as simply part of getting old as there are many treatments available that can slow or mitigate symptoms and give people a better quality of life.

'People must get it checked out,' he said.