The Big Bang Theory, The Itchy Brain Simulation

Leonard is away at sea, so Sheldon and Penny spend time together and spill some revealing secrets. Meanwhile, Howard comes to Raj's aid after his breakup with his girlfriend.

Leonard returns from the North Sea expedition and finds things chilly between him and Sheldon, while Howard's relationship with his mother opens the door to questions about his masculinity.

Raj puts together a scavenger hunt that turns into serious, cutthroat competition among the gang.

Sheldon is fit to be tied when Amy ruins one of his favourite adventure films, while Leonard finds the key to getting Penny to do his bidding, and Raj and Stuart get creative with their online-dating profiles.

Amy takes a job at Sheldon's university, putting their relationship to the test.

Sheldon makes a major scientific breakthrough, but he feels it may haunt him for the rest of his career. Meanwhile, Howard makes a grand romantic gesture to Bernadette, which causes Penny to put more effort into her relationship with Leonard.

When Sheldon's childhood hero, Professor Proton, seeks Leonard's help with an experiment, the slighted Sheldon goes nuclear and decides to get revenge by befriending another TV science guy.

Leonard fails to stop Sheldon from overreacting after a past slight comes to light, and as punishment Leonard must walk a mile in Sheldon's shoes. Meanwhile, Penny has a run-in with Raj's former girlfriend Lucy.

Howard's mother has a say when he and Bernadette host Thanksgiving dinner for the gang.

When Sheldon's accidental scientific discovery is disproved, Amy and Leonard try to help him deal with the shame and the disappointment. Meanwhile, Howard and Bernadette open their home to Raj for a week.

With Sheldon in Texas, the gang gathers to decorate for Christmas, and they each contemplate if they would have had a wonderful life had they never met him.

Penny turns to Leonard for comfort after her guest appearance on NCIS does not turn out well. She ends up putting Leonard on the spot regarding their relationship. Sheldon works on his sense of humor, and Raj practices talking to girls.

There's impactful news on the work front as Penny makes a big step toward pursuing a full-time acting career, and Sheldon is forced to take a vacation.

Unable to score tickets for Comic-Con, Sheldon decides to stage his own comic-book convention, while the ladies attempt to act like grown ups.

Amy has amour on her mind when she talks Sheldon into a romantic Valentine's Day getaway to Napa Valley wine country. Back at home, Leonard and Penny make an emergency visit to the vet with Raj's dog.

Leonard's purchase of a dining-room table for the apartment doesn't sit well with Sheldon, so much so that it forces him to reevaluate his life. Meanwhile, Bernadette isn't quite over the moon about Howard taking another trip to space.

Things turn rocky between Sheldon and Wolowitz after a barrage of insults, and Bernadette steps in to mediate a peace. Meanwhile, Penny is offered a movie role that may prove embarrassing.

While Sheldon and Howard continue their bonding, Sheldon's visit to see his mommy forces him to start addressing a new reality. The gang are subjected to a murder mystery party that leads them to speculate where they might be in 20 years.

Raj wrestles with dating two women at the same time, Penny is offered a part in a trashy movie, and Sheldon can't decide between two gaming systems.

Raj and Howard double-date, and the latter is flushed with embarrassment after Raj's girlfriend reveals a secret she knows about Howard.

Leonard reinstates Anything Can Happen Thursday, and it leads the regimented Sheldon to attempt something spontaneous, which creates friction among Penny, Amy and Bernadette. Raj requests help from Howard in prepping for a date with Emily.

Sheldon receives counseling from his childhood TV idol, Professor Proton, while Penny and Leonard reach a relationship milestone and turn it into a competition. Also, Bernadette and Amy turn Star Wars Day into a special event for the guys.

A trying day at the movie shoot leaves Penny with questions about her life choices, so she decides to act on it. Caring for a bedridden Mrs Wolowitz proves a challenge for Howard and Bernadette.

Sheldon gets caught up in all the life-altering changes going on around him and considers a monumental move.