more recently, goldman-rakic and colleagues (1993) evoked short-term memory loss in localized regions of space by temporary inactivation of portions of the dlpfc. once the concept of working memory (see also baddeley's model of working memory) was established in contemporary neuroscience by alan baddeley (1986), these neuropsychological findings contributed to the theory that the prefrontal cortex implements working memory and, in some extreme formulations, only working memory. in the 1990s this theory developed a wide following, and it became the predominant theory of pf function, especially for nonhuman primates. the concept of working memory used by proponents of this theory focused mostly on the short-term maintenance of information, and rather less on the manipulation or monitoring of such information or on the use of that information for decisions. consistent with the idea that the prefrontal cortex functions predominantly in maintenance memory, delay-period activity in the pf has often been interpreted as a memory trace. (the phrase "delay-period activity" applies to neuronal activity that follows the transient presentation of an instruction cue and persists until a subsequent "go" or "trigger" signal.) to explore alternative interpretations of delay-period activity in the prefrontal cortex, lebedev et al. (2004) investigated the discharge rates of single prefrontal neurons as monkeys attended to a stimulus marking one location while remembering a different, unmarked location. both locations served as potential targets of a saccadic eye movement. although the task made intensive demands on short-term memory, the largest proportion of prefrontal neurons represented attended locations, not remembered ones. these findings showed that short-term memory functions cannot account for all, or even most, delay-period activity in the part of the prefrontal cortex explored. the authors suggested that prefrontal activity during the delay-period contributes more to the process of attentional selection (and selective attention) than to memory storage. speech production and language various areas of the prefrontal cortex have been implicated in a multitude of critical functions regarding speech production, language comprehension, and response planning before speaking. cognitive neuroscience has shown that the left ventrolateral prefrontal cortex is vital in the processing of words and sentences. the right prefrontal cortex has been found to be responsible for coordinating the retrieval of explicit memory for use in speech, whereas the deactivation of the left is responsible for mediating implicit memory retrieval to be used in verb generation. recollection of nouns (explicit memory) is impaired in some amnesic patients with damaged right prefrontal cortices, but verb generation remains intact because of its reliance on left prefrontal deactivation. many researchers now include ba45 in the prefrontal cortex because together with ba44 it makes up an area of the frontal lobe called broca's area. broca's area is widely considered the output area of the language production pathway in the brain (as opposed to wernicke's area in the medial temporal lobe, which is seen as the language input area). ba45 has been shown to be implicated for the retrieval of relevant semantic knowledge to be used in conversation/speech. the right lateral prefrontal cortex (rlpfc) is implicated in the planning of complex behavior, and together with bilateral ba45, they act to maintain focus and coherence during speech production. however, left ba45 has been shown to be activated significantly while maintaining speech coherence in young people. older people have been shown to recruit the right ba45 more so than their younger counterparts. this aligns with the evidence of decreased lateralization in other brain systems during aging. in addition, this increase in ba45 and rlpfc activity in combination of ba47 in older patients has been shown to contribute to “off-topic utterances.” the ba47 area in the prefrontal cortex is implicated in “stimulus-driven” retrieval of less-salient knowledge than is required to contribute to a conversation. in other words, elevated activation of the ba47 together with altered activity in ba45 and the broader rlpfc has been shown to contribute to the inclusion of less relevant information and irrelevant tangential conversational speech patterns in older subjects. clinical significance