Is there a name for the thing in your mind that causes smells to bring back memories?

its called Proustian Memory.

Involuntary memory (fr. mémoire involontaire) is a concept made famous by the French writer Marcel Proust in his novel In Search of Lost Time, although the idea was also developed in his earlier writings, Contre Sainte-Beuve and Jean Santeuil. It is sometimes referred to as "Proustian memory."

Proust contrasts involuntary memory with voluntary memory. The latter designates memories retrieved by "intelligence," that is, memories produced when we put conscious effort into remembering events, people, and places. Proust's narrator laments that such memories are inevitably partial, and do not bear the "essence" of the past. The most famous instance of involuntary memory in Proust is known as the "episode of the madeleine," but there are at least half of a dozen in In Search of Lost Time, including the memories produced by the scent of a public lavatory on the Champs-Élysées.[citation needed]

The function of involuntary memory in the novel is not self-evident, however.[weasel words] It has been argued[who?] that involuntary memory unlocks the Narrator's past as the subject of his novel, but also that he does not begin writing until many years after the episode of the madeleine, for example. Other critics have suggested that it is not the recovery of the past per se that is significant for the Narrator, but rather the happiness produced by his recognition of the past in a present moment. Maurice Blanchot in Le Livre à venir points out that involuntary memories are epiphanic and pointed, and cannot effectively support a sustained narrative. He notes that the difference between Proust's uncompleted Jean Santeuil and In Search of Lost Time is the voluntary memories that provide the connective tissue between such moments and make up the vast bulk of the narrative of the later novel.[improper synthesis?]

A contemporary influence on Proust's conception of involuntary memory may have been his cousin, the French philosopher Henri Bergson, who in Matter and Memory (1906) made a distinction between two types of memory, the habit of memory as in learning a poem by heart, and spontaneous memory that stores up perceptions and impressions and reveals them in sudden flashes. However, Proust criticism of the last quarter century has tended to discount the influence of Bergson on Proust's ideas.